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Sample records for ac external magnetic

  1. Numerical and theoretical evaluations of AC losses for single and infinite numbers of superconductor strips with direct and alternating transport currents in external AC magnetic field

    NASA Astrophysics Data System (ADS)

    Kajikawa, K.; Funaki, K.; Shikimachi, K.; Hirano, N.; Nagaya, S.

    2010-11-01

    AC losses in a superconductor strip are numerically evaluated by means of a finite element method formulated with a current vector potential. The expressions of AC losses in an infinite slab that corresponds to a simple model of infinitely stacked strips are also derived theoretically. It is assumed that the voltage-current characteristics of the superconductors are represented by Bean’s critical state model. The typical operation pattern of a Superconducting Magnetic Energy Storage (SMES) coil with direct and alternating transport currents in an external AC magnetic field is taken into account as the electromagnetic environment for both the single strip and the infinite slab. By using the obtained results of AC losses, the influences of the transport currents on the total losses are discussed quantitatively.

  2. AC photovoltaic module magnetic fields

    SciTech Connect

    Jennings, C.; Chang, G.J.; Reyes, A.B.; Whitaker, C.M.

    1997-12-31

    Implementation of alternating current (AC) photovoltaic (PV) modules, particularly for distributed applications such as PV rooftops and facades, may be slowed by public concern about electric and magnetic fields (EMF). This paper documents magnetic field measurements on an AC PV module, complementing EMF research on direct-current PV modules conducted by PG and E in 1993. Although not comprehensive, the PV EMF data indicate that 60 Hz magnetic fields (the EMF type of greatest public concern) from PV modules are comparable to, or significantly less than, those from household appliances. Given the present EMF research knowledge, AC PV module EMF may not merit considerable concern.

  3. Martian external magnetic field proxies

    NASA Astrophysics Data System (ADS)

    Langlais, Benoit; Civet, Francois

    2015-04-01

    Mars possesses no dynamic magnetic field of internal origin as it is the case for the Earth or for Mercury. Instead Mars is characterized by an intense and localized magnetic field of crustal origin. This field is the result of past magnetization and demagnetization processes, and reflects its evolution. The Interplanetary Magnetic Field (IMF) interacts with Mars' ionized environment to create an external magnetic field. This external field is weak compared to lithospheric one but very dynamic, and may hamper the detailed analysis of the internal magnetic field at some places or times. Because there are currently no magnetic field measurements made at Mars' surface, it is not possible to directly monitor the external field temporal variability as it is done in Earth's ground magnetic observatories. In this study we examine to indirect ways of quantifying this external field. First we use the Advanced Composition Explorer (ACE) mission which measures the solar wind about one hour upstream of the bow-shock resulting from the interaction between the solar wind and the Earth's internal magnetic field. These measurements are extrapolated to Mars' position taking into account the orbital configurations of the Mars-Earth system and the velocity of particles carrying the IMF. Second we directly use Mars Global Surveyor magnetic field measurements to quantify the level of variability of the external field. We subtract from the measurements the internal field which is otherwise modeled, and bin the residuals first on a spatial and then on a temporal mesh. This allows to compute daily or semi daily index. We present a comparison of these two proxies and demonstrate their complementarity. We also illustrate our analysis by comparing our Martian external field proxies to terrestrial index at epochs of known strong activity. These proxies will especially be useful for upcoming magnetic field measurements made around or at the surface of Mars.

  4. Reentrant ac Magnetic Susceptibility in Josephson-Junction Arrays

    SciTech Connect

    Araujo-Moreira, F.M.; Barbara, P.; Cawthorne, A.B.; Lobb, C.J.

    1997-06-01

    We have measured the complex ac magnetic susceptibility of unshunted Josephson-junction arrays as a function of temperature T , amplitude of the excitation field h{sub ac} , and external magnetic field H{sub dc} . For small h{sub ac} Meissner screening occurs. For larger h{sub ac} , however, the screening is reentrant in T . This reentrance is not thermodynamic but dynamic and arises from the paramagnetic contribution of multijunction loops. This result gives an alternative explanation of the paramagnetic Meissner effect observed in granular superconductors. Experimental results are in agreement with a simplified model based on a single loop containing four junctions. {copyright} {ital 1997} {ital The American Physical Society}

  5. Ac magnetic susceptibility study of in vivo nanoparticle biodistribution

    NASA Astrophysics Data System (ADS)

    Gutiérrez, L.; Mejías, R.; Barber, D. F.; Veintemillas-Verdaguer, S.; Serna, C. J.; Lázaro, F. J.; Morales, M. P.

    2011-06-01

    We analysed magnetic nanoparticle biodistribution, before and after cytokine conjugation, in a mouse model by ac susceptibility measurements of the corresponding resected tissues. Mice received repeated intravenous injections of nanoparticle suspension for two weeks and they were euthanized 1 h after the last injection. In general, only 10% of the total injected nanoparticles after multiple exposures were found in tissues. The rest of the particles may probably be metabolized or excreted by the organism. Our findings indicate that the adsorption of interferon to DMSA-coated magnetic nanoparticles changes their biodistribution, reducing the presence of nanoparticles in lungs and therefore their possible toxicity. The specific targeting of the particles to tumour tissues by the use of an external magnetic field has also been studied. Magnetic nanoparticles were observed by transmission electron microscopy in the targeted tissue and quantified by ac magnetic susceptibility.

  6. 21 CFR 886.4440 - AC-powered magnet.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ... 21 Food and Drugs 8 2012-04-01 2012-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food... DEVICES OPHTHALMIC DEVICES Surgical Devices § 886.4440 AC-powered magnet. (a) Identification. An AC-powered magnet is an AC-powered device that generates a magnetic field intended to find and...

  7. 21 CFR 886.4440 - AC-powered magnet.

    Code of Federal Regulations, 2011 CFR

    2011-04-01

    ... 21 Food and Drugs 8 2011-04-01 2011-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food... DEVICES OPHTHALMIC DEVICES Surgical Devices § 886.4440 AC-powered magnet. (a) Identification. An AC-powered magnet is an AC-powered device that generates a magnetic field intended to find and...

  8. 21 CFR 886.4440 - AC-powered magnet.

    Code of Federal Regulations, 2014 CFR

    2014-04-01

    ... 21 Food and Drugs 8 2014-04-01 2014-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food... DEVICES OPHTHALMIC DEVICES Surgical Devices § 886.4440 AC-powered magnet. (a) Identification. An AC-powered magnet is an AC-powered device that generates a magnetic field intended to find and...

  9. 21 CFR 886.4440 - AC-powered magnet.

    Code of Federal Regulations, 2013 CFR

    2013-04-01

    ... 21 Food and Drugs 8 2013-04-01 2013-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food... DEVICES OPHTHALMIC DEVICES Surgical Devices § 886.4440 AC-powered magnet. (a) Identification. An AC-powered magnet is an AC-powered device that generates a magnetic field intended to find and...

  10. 21 CFR 886.4440 - AC-powered magnet.

    Code of Federal Regulations, 2010 CFR

    2010-04-01

    ... 21 Food and Drugs 8 2010-04-01 2010-04-01 false AC-powered magnet. 886.4440 Section 886.4440 Food... DEVICES OPHTHALMIC DEVICES Surgical Devices § 886.4440 AC-powered magnet. (a) Identification. An AC-powered magnet is an AC-powered device that generates a magnetic field intended to find and...

  11. Physical aspects of magnetic hyperthermia: Low-frequency ac field absorption in a magnetic colloid

    NASA Astrophysics Data System (ADS)

    L. Raikher, Yu.; Stepanov, V. I.

    2014-11-01

    A uniaxially anisotropic superparamagnetic particle suspended in a viscous fluid and subjected to an ac field is considered. Consistently taking into account both internal (Néel) and external (Brownian) magnetic relaxations, a simple expression for the dynamic susceptibility is obtained. This result, with regard to the ac field energy absorption, is compared to the common heuristic approach. This is done for a model polydisperse colloid containing maghemite nanoparticles, which are assumed to posses either bulk or surface magnetic anisotropy. It is shown that viscous losses caused by the particle motion in a fluid matrix make important contribution to the full magnetic response of a ferrocolloid and, thus, its ability to absorb the ac field energy. The obtained exact expression, which takes in both dissipation mechanisms, paves the way to correct optimization of the nanoparticle-mediated heating effect.

  12. AC magnetic susceptibility of Bi2223-system

    NASA Astrophysics Data System (ADS)

    Kimishima, Y.; Inagaki, K.; Tanabe, K.; Nagata, N.; Ichiyanagi, Y.

    1998-01-01

    The AC magnetic susceptibilities χ AC of a Bi2223 sintered sample were measured by the Hartshorn bridge method. The linear AC χ' 0 showed the two-steps behavior at T C1 and T C2, where T C1 > T C2. The χ'0-data between T C1 and T C2 has no H AC-dependence and agreed well with those of powder specimen, and they can be regarded as the intragrain magnetic susceptibility. Below the inter-grain transition temperature T C2 the χ″ 0 showed a positive peak. The temperature dependence of χ' 0 and χ″ 0 were analyzed by the Bean's critical-state model. As a result, the temperature dependence of critical current density J C ∝ (1 - T/T C2) β was obtained with β = 2.3-2.6. The non-linear χ' 2 and χ″ 2 below T C2 resemble the behaviors derived from the Bean model, but the negative divergence of χ' 2 may show the evidence of d-wave paring in the present Bi2223-system.

  13. External-field-free magnetic biosensor

    SciTech Connect

    Li, Yuanpeng; Wang, Yi; Klein, Todd; Wang, Jian-Ping

    2014-03-24

    In this paper, we report a magnetic nanoparticle (MNP) detection scheme without the presence of any external magnetic field. The proposed magnetic sensor uses a patterned groove structure within the sensor so that no external magnetic field is needed to magnetize the MNPs. An example is given based on a giant magnetoresistance (GMR) sensing device with a spin valve structure. For this structure, the detection of MNPs located inside the groove and near the free layer is demonstrated under no external magnetic field. Micromagnetic simulations are performed to calculate the signal to noise level of this detection scheme. A maximum signal to noise ratio (SNR) of 18.6 dB from one iron oxide magnetic nanoparticle with 8 nm radius is achieved. As proof of concept, this external-field-free GMR sensor with groove structure of 200 nm × 200 nm is fabricated using a photo and an electron beam integrated lithography process. Using this sensor, the feasibility demonstration of the detection SNR of 9.3 dB is achieved for 30 μl magnetic nanoparticles suspension (30 nm iron oxide particles, 1 mg/ml). This proposed external-field-free sensor structure is not limited to GMR devices and could be applicable to other magnetic biosensing devices.

  14. Trapped Field Attenuation Characteristics of HTS Bulk Magnet Exposed to External Traveling-Wave Magnetic Field in an HTSLSM

    NASA Astrophysics Data System (ADS)

    Jin, Jianxun; Zheng, Luhai

    Traveling-wave magnetic field generated by a linear motor is a typical AC time-varying field. In order to identify the trapped magnetic flux attenuation characteristics of the high temperature superconducting (HTS) bulk magnet exposed to the external traveling-wave field generated by the primary of a developed HTS linear synchronous motor (HTSLSM), relevant experiments have been carried out through a built measurement system. As results, the relationships between the trapped magnetic flux attenuation of the HTS bulk magnet and the amplitude, frequency and direction of the external traveling-wave magnetic field are experimentally obtained to allow the HTSLSM characteristics to be practically verified.

  15. QCD quark condensate in external magnetic fields

    NASA Astrophysics Data System (ADS)

    Bali, G. S.; Bruckmann, F.; Endrődi, G.; Fodor, Z.; Katz, S. D.; Schäfer, A.

    2012-10-01

    We present a comprehensive analysis of the light condensates in QCD with 1+1+1 sea quark flavors (with mass-degenerate light quarks of different electric charges) at zero and nonzero temperatures of up to 190 MeV and external magnetic fields B<1GeV2/e. We employ stout smeared staggered fermions with physical quark masses and extrapolate the results to the continuum limit. At low temperatures we confirm the magnetic catalysis scenario predicted by many model calculations while around the crossover the condensate develops a complex dependence on the external magnetic field, resulting in a decrease of the transition temperature.

  16. Magnetic deflagration in the molecular magnet manganese-12-ac

    NASA Astrophysics Data System (ADS)

    McHugh, Sean

    In 1995, Paulsen and Park [1, 2] observed abrupt spontaneous reversals of the magnetization in crystals of the molecular magnet Mn12-ac, which they dubbed "magnetic avalanches". They suggested that the magnetic avalanches were a thermal runaway process where the reversing spins release heat stimulating further relaxation. Various exotic phenomena were proposed as an alternative explanations [3]. In 2005, Suzuki et al. [4] established that this spontaneous magnetic relaxation occurs as a "front" separating regions of opposing magnetization that propagates at a constant speed through the crystal. They suggested that this propagating front is analogous to a flame in chemical deflagration and introduced the thermal relaxation process, magnetic deflagration. The analysis presented there was limited by lack of data. A more thorough comparison with the theory would require the ability to trigger avalanches in a more controlled way rather than wait for their spontaneous occurrence. The work presented in this thesis is a continuation of the program initiated by Suzuki [4, 5]. Significant progress experimental progress has been made allowing us to trigger avalanches over a wide range of conditions. The magnetization dynamics and the ignition temperatures are studied in detail using an array of micro-sized Hall sensors and Germanium thermometers. In addition, we report the existence of a new species of avalanches consisting only of the fast-relaxing isomers of Mn12-ac, the so-called "minor species". We explore avalanches of both species, as well as the interaction between them. Finally, a detailed analysis is performed to compare the experiment with the theory of magnetic deflagration [6]. We find the theory of magnetic deflagration to be consistent with the data and extract values for the key physical quantities: the thermal diffusivity and avalanche front temperatures. Agreement between our predicted values and an independent measurement of these quantities would provide

  17. ac electroosmotic pumping induced by noncontact external electrodes

    PubMed Central

    Wang, Shau-Chun; Chen, Hsiao-Ping; Chang, Hsueh-Chia

    2007-01-01

    Electroosmotic (EO) pumps based on dc electroosmosis is plagued by bubble generation and other electrochemical reactions at the electrodes at voltages beyond 1 V for electrolytes. These disadvantages limit their throughput and offset their portability advantage over mechanical syringe or pneumatic pumps. ac electroosmotic pumps at high frequency (>100 kHz) circumvent the bubble problem by inducing polarization and slip velocity on embedded electrodes,1 but they require complex electrode designs to produce a net flow. We report a new high-throughput ac EO pump design based on induced-polarization on the entire channel surface instead of just on the electrodes. Like dc EO pumps, our pump electrodes are outside of the load section and form a cm-long pump unit consisting of three circular reservoirs (3 mm in diameter) connected by a 1×1 mm channel. The field-induced polarization can produce an effective Zeta potential exceeding 1 V and an ac slip velocity estimated as 1 mm∕sec or higher, both one order of magnitude higher than earlier dc and ac pumps, giving rise to a maximum throughput of 1 μl∕sec. Polarization over the entire channel surface, quadratic scaling with respect to the field and high voltage at high frequency without electrode bubble generation are the reasons why the current pump is superior to earlier dc and ac EO pumps. PMID:19693362

  18. Analysis of magnetic refrigeration with external regeneration

    NASA Astrophysics Data System (ADS)

    Jaeger, Steven R.; Barclay, John A.; Overton, William C., Jr.

    A simplified computer model of a typical magnetic refrigerator using external regeneration is used to investigate different magnetic materials and refrigerator designs. It was found that nonideal temperature-entropy properties of the magnetic material and nonideal regeneration both contribute significantly to reducing the useful range and efficiency of these refrigerators. While the model cannot be used to predict the performance of actual refrigerators, it provides a quick means of evaluating whether inherent limitations, as a result of the choice of the magnetic material or the regenerator design, will make it impossible for a specific design to satisfy the requirements for a given application. Preliminary results from using this model with an approximate model for GdNi as the magnetic material are presented.

  19. AC current distribution and losses in multifilamentary superconductors exposed to longitudinal magnetic field

    SciTech Connect

    Le Naour, S.; Lacaze, A.; Laumond, Y.; Estop, P.; Verhaege, T.

    1996-07-01

    The current distribution and also AC losses, in a multifilamentary superconductor carrying a transport current, are influenced by the self and the external magnetic field. By using the Maxwell equations, a model has been developed in order to calculate the temporal evolution of current distribution in a single wire exposed or not to external magnetic field. This model is based on the actual relationship of electrical field E with current density J and takes into account the twist pitch of the wire. AC losses are calculated by adding all local losses through the cross section. This paper presents calculations of the influence of the cable twist coupled with the longitudinal magnetic field, and also gives some ideas how to decrease losses.

  20. External Magnetic Field Reduction Techniques for the Advanced Stirling Radioisotope Generator

    NASA Technical Reports Server (NTRS)

    Niedra, Janis M.; Geng, Steven M.

    2013-01-01

    Linear alternators coupled to high efficiency Stirling engines are strong candidates for thermal-to-electric power conversion in space. However, the magnetic field emissions, both AC and DC, of these permanent magnet excited alternators can interfere with sensitive instrumentation onboard a spacecraft. Effective methods to mitigate the AC and DC electromagnetic interference (EMI) from solenoidal type linear alternators (like that used in the Advanced Stirling Convertor) have been developed for potential use in the Advanced Stirling Radioisotope Generator. The methods developed avoid the complexity and extra mass inherent in data extraction from multiple sensors or the use of shielding. This paper discusses these methods, and also provides experimental data obtained during breadboard testing of both AC and DC external magnetic field devices.

  1. Calorimetric method of ac loss measurement in a rotating magnetic field.

    PubMed

    Ghoshal, P K; Coombs, T A; Campbell, A M

    2010-07-01

    A method is described for calorimetric ac-loss measurements of high-T(c) superconductors (HTS) at 80 K. It is based on a technique used at 4.2 K for conventional superconducting wires that allows an easy loss measurement in parallel or perpendicular external field orientation. This paper focuses on ac loss measurement setup and calibration in a rotating magnetic field. This experimental setup is to demonstrate measuring loss using a temperature rise method under the influence of a rotating magnetic field. The slight temperature increase of the sample in an ac-field is used as a measure of losses. The aim is to simulate the loss in rotating machines using HTS. This is a unique technique to measure total ac loss in HTS at power frequencies. The sample is mounted on to a cold finger extended from a liquid nitrogen heat exchanger (HEX). The thermal insulation between the HEX and sample is provided by a material of low thermal conductivity, and low eddy current heating sample holder in vacuum vessel. A temperature sensor and noninductive heater have been incorporated in the sample holder allowing a rapid sample change. The main part of the data is obtained in the calorimetric measurement is used for calibration. The focus is on the accuracy and calibrations required to predict the actual ac losses in HTS. This setup has the advantage of being able to measure the total ac loss under the influence of a continuous moving field as experienced by any rotating machines. PMID:20687748

  2. Calorimetric method of ac loss measurement in a rotating magnetic field

    NASA Astrophysics Data System (ADS)

    Ghoshal, P. K.; Coombs, T. A.; Campbell, A. M.

    2010-07-01

    A method is described for calorimetric ac-loss measurements of high-Tc superconductors (HTS) at 80 K. It is based on a technique used at 4.2 K for conventional superconducting wires that allows an easy loss measurement in parallel or perpendicular external field orientation. This paper focuses on ac loss measurement setup and calibration in a rotating magnetic field. This experimental setup is to demonstrate measuring loss using a temperature rise method under the influence of a rotating magnetic field. The slight temperature increase of the sample in an ac-field is used as a measure of losses. The aim is to simulate the loss in rotating machines using HTS. This is a unique technique to measure total ac loss in HTS at power frequencies. The sample is mounted on to a cold finger extended from a liquid nitrogen heat exchanger (HEX). The thermal insulation between the HEX and sample is provided by a material of low thermal conductivity, and low eddy current heating sample holder in vacuum vessel. A temperature sensor and noninductive heater have been incorporated in the sample holder allowing a rapid sample change. The main part of the data is obtained in the calorimetric measurement is used for calibration. The focus is on the accuracy and calibrations required to predict the actual ac losses in HTS. This setup has the advantage of being able to measure the total ac loss under the influence of a continuous moving field as experienced by any rotating machines.

  3. Calorimetric method of ac loss measurement in a rotating magnetic field

    SciTech Connect

    Ghoshal, P. K.; Coombs, T. A.; Campbell, A. M.

    2010-07-15

    A method is described for calorimetric ac-loss measurements of high-T{sub c} superconductors (HTS) at 80 K. It is based on a technique used at 4.2 K for conventional superconducting wires that allows an easy loss measurement in parallel or perpendicular external field orientation. This paper focuses on ac loss measurement setup and calibration in a rotating magnetic field. This experimental setup is to demonstrate measuring loss using a temperature rise method under the influence of a rotating magnetic field. The slight temperature increase of the sample in an ac-field is used as a measure of losses. The aim is to simulate the loss in rotating machines using HTS. This is a unique technique to measure total ac loss in HTS at power frequencies. The sample is mounted on to a cold finger extended from a liquid nitrogen heat exchanger (HEX). The thermal insulation between the HEX and sample is provided by a material of low thermal conductivity, and low eddy current heating sample holder in vacuum vessel. A temperature sensor and noninductive heater have been incorporated in the sample holder allowing a rapid sample change. The main part of the data is obtained in the calorimetric measurement is used for calibration. The focus is on the accuracy and calibrations required to predict the actual ac losses in HTS. This setup has the advantage of being able to measure the total ac loss under the influence of a continuous moving field as experienced by any rotating machines.

  4. External dc bias field effects in the nonlinear ac stationary response of permanent dipoles in a uniaxial potential

    NASA Astrophysics Data System (ADS)

    Wei, Nijun; Coffey, William T.; Déjardin, Pirre-Michel; Kalmykov, Yuri P.

    External dc bias field effects on the nonlinear dielectric relaxation and dynamic Kerr effect of a system of permanent dipoles in a uniaxial mean field potential are studied via the rotational Brownian motion model. Postulated in terms of the infinite hierarchy of differential-recurrence equations for the statistical moments (the expectation value of the Legendre polynomials), the dielectric and Kerr effect ac stationary responses may be evaluated for arbitrary dc bias field strength via perturbation theory in the ac field. We have given two complementary approaches for treating the nonlinear effects. The first is based on perturbation theory allowing one to calculate the nonlinear ac stationary responses using powerful matrix methods. The second approach based on the accurate two-mode approximation [D.A. Garanin, Phys. Rev. E. 54, 3250 (1996)] effectively generalizes the existing results for dipolar systems in superimposed ac and dc fields to a mean field potential. The results apply both to nonlinear dielectric relaxation and dynamic Kerr effect of nematics and to magnetic birefringence relaxation of ferrofluids. Furthermore, the given methods of the solution of infinite hierarchies of multi-term recurrence relations are quite general and can be applied to analogous nonlinear response problems.

  5. AC Loss Analysis on the Superconducting Coupling Magnet in MICE

    SciTech Connect

    Wu, Hong; Wang, Li; Green, Michael; Li, LanKai; Xu, FengYu; Liu, XiaoKun; Jia, LinXinag

    2008-07-08

    A pair of coupling solenoids is used in MICE experiment to generate magnetic field which keeps the muons within the iris of thin RF cavity windows. The coupling solenoids have a 1.5-meter inner diameter and will produce 7.4 T peak magnetic field. Three types of AC losses in coupling solenoid are discussed. The affect of AC losses on the temperature distribution within the cold mass during charging and rapid discharging process is analyzed also. The analysis result will be further confirmed by the experiment of the prototype solenoid for coupling solenoid, which will be designed, fabricated and tested at ICST.

  6. Secondary resonance magnetic force microscopy using an external magnetic field for characterization of magnetic thin films

    NASA Astrophysics Data System (ADS)

    Liu, Dongzi; Mo, Kangxin; Ding, Xidong; Zhao, Liangbing; Lin, Guocong; Zhang, Yueli; Chen, Dihu

    2015-09-01

    A bimodal magnetic force microscopy (MFM) that uses an external magnetic field for the detection and imaging of magnetic thin films is developed. By applying the external modulation magnetic field, the vibration of a cantilever probe is excited by its magnetic tip at its higher eigenmode. Using magnetic nanoparticle samples, the capacity of the technique which allows single-pass imaging of topography and magnetic forces is demonstrated. For the detection of magnetic properties of thin film materials, its signal-to-noise ratio and sensitivity are demonstrated to be superior to conventional MFM in lift mode. The secondary resonance MFM technique provides a promising tool for the characterization of nanoscale magnetic properties of various materials, especially of magnetic thin films with weak magnetism.

  7. Super-resolution high sensitivity AC Magnetic Field Imaging with NV Centers in Diamond

    NASA Astrophysics Data System (ADS)

    Bauch, Erik; Jaskula, Jean-Christophe; Trifonov, Alexei; Walsworth, Ronald

    2015-05-01

    The Nitrogen-Vacancy center in diamond (NV center), a defect consisting of a nitrogen atom next to a missing atom, has been successfully applied to sense magnetic field, electric field, temperature and can also be used as fluorescence marker and single photon emitter. We will present super-resolution imaging of NV centers and simultaneous sensing of AC magnetic fields with high sensitivity. To demonstrate the applicability of super-resolution magnetic field imaging, we resolve several NV centers with an optical resolution smaller than 20 nm and probe locally the gradient of a externally applied magnetic field. Additionally, we demonstrate the detection of magnetic field signals from 1H protons with subdiffraction image resolution. We will also show that our super-resolution magnetometer will benefit from a new readout method based on a spin-to-charge mapping that we have developed to increase the readout contrast.

  8. Time-resolved Measurements of Spontaneous Magnetic Deflagration of Mn12 tBuAc

    NASA Astrophysics Data System (ADS)

    Chen, Yizhang; Kent, A. D.; Zhang, Qing; Sarachik, M. P.; Baker, M. L.; Garanin, D. A.; Mhesn, Najah; Lampropoulos, Christos

    Magnetic deflagration in molecular magnets has been triggered by heat pulses and acoustic waves. In this work we report spontaneous magnetic deflagration (i.e. deflagration that occurs without an external trigger) in the axially symmetric single molecule magnet Mn12 tBuAc . Magnetic hysteresis measurements show steps due to resonant quantum tunneling (RQT) below 1K, confirming the spin-Hamiltonian parameters for this material and previous results. Deflagration speeds measured with a newly constructed higher bandwidth (2MHz) setup will be presented as a function of transverse and longitudinal fields Hx ⊗Hz both on and off resonance. A large increase in front velocity near RQT steps is observed in experiments with swept transverse fields and will be discussed in light of models of deflagration. Work supported by NSF-DMR-1309202 (NYU); ARO W911NF-13-1-0125 (CCNY); DMR-1161571(Lehman); Cottrell College Science Award (UNF).

  9. Magnetic flux penetration into twisted multifilamentary coated superconductors subjected to ac transverse magnetic fields

    NASA Astrophysics Data System (ADS)

    Amemiya, Naoyuki; Sato, Susumu; Ito, Takeshi

    2006-12-01

    ac losses in superconductors are generated by the magnetic flux and current penetration into them. To reveal the magnetic flux and current penetration processes in twisted multifilamentary coated superconductors in which the thin superconductor layer is subdivided into filaments and then twisted as a whole for ac loss reduction, a theoretical model for electromagnetic field analysis was developed based on the power law E-J (electric-field-current-density) characteristic for the superconductor and a thin strip approximation of the conductor. The developed theoretical model was implemented into a numerical code using the finite element method to calculate and visualize the current and magnetic flux distributions. The magnetization losses in twisted multifilamentary coated superconductors exposed to ac transverse magnetic fields were calculated from the temporal evolutions of the current distribution to demonstrate the effect of the twisted multifilamentary architecture on ac loss reduction.

  10. Towards real-time Martian external magnetic field proxies

    NASA Astrophysics Data System (ADS)

    Langlais, B.; Civet, F.

    2015-10-01

    Mars possesses no dynamic magnetic field of internal origin as it is the case for the Earth or for Mercury.Instead Mars is characterized by an intense and localized magnetic field of crustal origin. This field is the result of past magnetization and demagnetization processes, and reflects its evolution. The Interplanetary Magnetic Field (IMF) interacts with Mars' ionized environment to create an external magnetic field. This external field is weak compared to lithospheric one but very dynamic, and may hamper the detailed analysis of the internal magnetic field at some places or times. Because there are currently no magnetic field measurements made at Mars' surface, it is not possible to directly monitor the external field temporal variability as it is done in Earth's ground magnetic observatories. In this study we examine two indirect ways of quantifying this external field. First we use the Advanced Composition Explorer (ACE) mission which measures the solar wind about one hour upstream of the bow-shock resulting from the interaction between the solar wind and the Earth's internal magnetic field and extrapolate these measurements to Mars. Second we directly use Mars Global Surveyor magnetic field measurements to quantify the level of variability of the external field on a daily basis. We present a comparison of these two proxies and demonstrate their complementarity. These proxies will especially be useful for upcoming magnetic field measurements made around or at the surface of Mars.

  11. Monitoring colloidal stability of polymer-coated magnetic nanoparticles using AC susceptibility measurements.

    PubMed

    Herrera, Adriana P; Barrera, Carola; Zayas, Yashira; Rinaldi, Carlos

    2010-02-15

    The application of the response of magnetic nanoparticles to oscillating magnetic fields to probe transitions in colloidal state and structure of polymer-coated nanoparticles is demonstrated. Cobalt ferrite nanoparticles with narrow size distribution were prepared and shown to respond to oscillating magnetic fields through a Brownian relaxation mechanism, which is dependent on the mechanical coupling between the particle dipoles and the surrounding matrix. These nanoparticles were coated with covalently-attached poly(N-isopropylacrylamide) (pNIPAM) or poly(N-isopropylmethacrylamide) (pNIPMAM) through free radical polymerization. The temperature induced transitions of colloidal suspensions of these nanoparticles were studied through a combination of differential scanning calorimetry (DSC), dynamic light scattering (DLS), and AC susceptibility measurements. In the pNIPAM coated nanoparticles excellent agreement was found for a transition temperature of approximately 30 degrees C by all three methods, although the AC susceptibility measurements indicated aggregation which was not evident from the DLS results. Small-angle neutron scattering (SANS) results obtained for pNIPAM coated nanoparticles confirmed that aggregation indeed occurs above the lower critical transition temperature of pNIPAM. For the pNIPMAM coated nanoparticles DLS and AC susceptibility measurements indicated aggregation at a temperature of approximately 33-35 degrees C, much lower than the transition temperature peak at 40 degrees C observed by DSC. However, the transition observed by DSC is very broad, hence it is possible that aggregation begins to occur at temperatures lower than the peak, as indicated by the AC susceptibility and DLS results. These experiments and observations demonstrate the possibility of using AC susceptibility measurements to probe transitions in colloidal suspensions induced by external stimuli. Because magnetic measurements do not require optical transparency, these

  12. Nonlinear magnetization relaxation of superparamagnetic nanoparticles in superimposed ac and dc magnetic bias fields

    NASA Astrophysics Data System (ADS)

    Titov, Serguey V.; Déjardin, Pierre-Michel; El Mrabti, Halim; Kalmykov, Yuri P.

    2010-09-01

    The nonlinear ac response of the magnetization M(t) of a uniaxially anisotropic superparamagnetic nanoparticle subjected to both ac and dc bias magnetic fields of arbitrary strengths and orientations is determined by averaging Gilbert’s equation augmented by a random field with Gaussian white-noise properties in order to calculate exactly the relevant statistical averages. It is shown that the magnetization dynamics of the uniaxial particle driven by a strong ac field applied at an angle to the easy axis of the particle (so that the axial symmetry is broken) alters drastically leading to different nonlinear effects due to coupling of the thermally activated magnetization reversal mode with the precessional modes of M(t) via the driving ac field.

  13. Nuclear magnetic resonance in magnets with a helicoidal magnetic structure in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Tankeyev, A. P.; Borich, M. A.; Smagin, V. V.

    2014-11-01

    In this review, the static and dynamic properties of a magnet with a helicoidal magnetic structure placed in an external magnetic field are discussed. The results of the investigation of its ground state and spectra, as well as the amplitudes of the spin excitations are presented. The temperature and field dependences of the basic thermodynamic characteristics (heat capacity, magnetization, and magnetic susceptibility) have been calculated in the spin-wave approximation. The results of calculating the local and integral dynamic magnetic susceptibility are given. This set of data represents a methodical basis for constructing a consistent (in the framework of unified approximations) picture of the NMR absorption in the magnet under consideration. Both local NMR characteristics (resonance frequency, line broadening, enhancement coefficient) and integral characteristics (resultant shape of the absorption line with its specific features) have been calculated. The effective Hamiltonian of the Suhl-Nakamura interaction of nuclear spins through spin waves has been constructed. The second moment and the local broadening of the line of the NMR absorption caused by this interaction have been calculated. The role of the basic local inhomogeneities in the formation of the integral line of the NMR absorption has been analyzed. The opportunities for the experimental NMR investigations in magnets with a chiral spin structure are discussed.

  14. Magnetization AC losses in MgB2 wires made by IMD process

    NASA Astrophysics Data System (ADS)

    Kováč, J.; Šouc, J.; Kováč, P.; Hušek, I.

    2015-01-01

    Magnetization AC losses of MgB2 superconductors with one and four filaments made by an internal magnesium diffusion (IMD) into boron process were measured and analyzed. For AC loss measurement a system based on a calibration-free method was used. Short samples of MgB2 wires were exposed to an external magnetic field with amplitudes up to 0.07 T, frequencies up to 1200 Hz, and a temperature range between 15 K and 40 K. A strong effect of eddy current losses was found in single-core wire containing pure copper sheath, which was proved by the same wire measurement after Cu etching. The impact of coupling current losses in non-twisted four-filament wire and the decoupling effect after twisting were observed. Coupling current losses in a low-frequency region were effectively reduced in agreement with theoretical assumption. The degradation of transport currents due to torsion stress by twisting was taken into account and the normalized AC losses of MgB2 wires made by IMD and powder-in-tube processes were compared. It appears that the IMD process is more perspective for AC applications due to much higher current densities and smaller degradation of current-carrying capability by twisting.

  15. Superconducting Sphere in an External Magnetic Field Revisited

    ERIC Educational Resources Information Center

    Sazonov, Sergey N.

    2013-01-01

    The purpose of this article is to give the intelligible procedure for undergraduate students to grasp proof of the fact that the magnetic field outside the hollow superconducting sphere (superconducting shell) coincides with the field of a point magnetic dipole both when an uniform external magnetic field is applied as when a ferromagnetic sphere…

  16. Exchange anisotropy determined by magnetic field dependence of ac susceptibility

    NASA Astrophysics Data System (ADS)

    Rodríguez-Suárez, R. L.; Vilela Leão, L. H.; de Aguiar, F. M.; Rezende, S. M.; Azevedo, A.

    2003-10-01

    ac susceptibility measurements of ferromagnetic/antiferromagnetic (FM/AF) bilayers are usually performed as a function of the temperature. In this work we describe measurements of transverse biased ac susceptibility (χt) of FM/AF bilayers as a function of the applied magnetic field H0. The measurements were carried out at room temperature by means of an ac magneto-optical Kerr effect susceptometer. The χt-1(H0) dependence, at the saturation magnetization regime, exhibits a linear behavior with the applied field parallel and perpendicular to the exchange bias direction. The linear extrapolation of χt-1 versus H0 cuts the abscissa at asymmetrical values of field due to the exchange bias coupling. The inverse susceptibility is calculated in the saturation regime by a model, which takes into account the free energy of both layers plus a term corresponding to the interfacial coupling. The exchange coupling field (HE) and uniaxial anisotropy (HU) are extracted from the best fit to the experimental results. The results obtained are crosschecked by those obtained from ferromagnetic resonance (FMR) and dc magnetometry. The measurements of the exchange bias and the uniaxial field in all of the three analyzed bilayers gave values that are consistently lower when measured by FMR than those obtained by ac and dc magnetometry. It is argued that the apparently discrepant values of HE and HU, obtained by different techniques, might be explained by existence of unstable AF grains at the AF/FM interface.

  17. AC Losses in the MICE Channel Magnets -- Is This a Curse or aBlessing?

    SciTech Connect

    Green, M.A.; Wu, H.; Wang, L.; Kai, L.L.; Jia, L.X.; Yang, S.Q.

    2008-01-31

    This report discusses the AC losses in the MICE channelmagnets during magnet charging and discharging. This report talks aboutthe three types of AC losses in the MICE magnets; the hysteretic AC lossin the superconductor, the coupling AC loss in the superconductor and theeddy current AC loss in the magnet mandrel and support structure. AClosses increase the heat load at 4 K. The added heat load increases thetemperature of the second stage of the cooler. In addition, AC losscontributes to the temperature rise between the second stage cold headand the high field point of the magnet, which is usually close to themagnet hot spot. These are the curses of AC loss in the MICE magnet thatcan limit the rate at which the magnet can be charge or discharged. Ifone is willing to allow some of the helium that is around the magnet toboil away during a magnet charge or discharge, AC losses can become ablessing. The boil off helium from the AC losses can be used to cool theupper end of the HTS leads and the surrounding shield. The AC losses arepresented for all three types of MICE magnets. The AC loss temperaturedrops within the coupling magnet are presented as an example of how boththe curse and blessing of the AC losses can be combined.

  18. Testing of a First Order AC Magnetic Susceptometer

    NASA Astrophysics Data System (ADS)

    Fukuda, Ryan; Sunny, Smitha; Ho, Pei-Chun

    2011-11-01

    A first-order AC magnetic susceptometer has been constructed and tested to find the magnetic response of strongly correlated electron materials. The instrument works by using a primary coil to apply a small AC magnetic field of .104 Oe to a sample with a cylindrical coil space of length .635 cm and diameter .355 cm. A lock-in amplifier is used to monitor the induced voltage from a set of secondary coils. By coupling a temperature-controlled system with this instrument, the change in the magnetic signal with respect to temperature is measured. Monitoring the signal changes may indicate the temperature that causes the material to transition to either a ferromagnetic, anti-ferromagnetic, or superconducting state. A 122.47 mg Gd polycrystal was used to test our susceptometer. The data qualitatively agrees with the previous results of magnetization vs. temperature of Gd single crystals by Nigh et al. [1]: there is a steep increase in the pick-up signal at 300 K where Gd becomes ferromagnetic and a peak at 210 K [1]. This susceptometer will be used for our future investigation of magnetic properties of rare earth compounds and nanoparticles in the temperature range of 10 K to 300 K. [4pt] [1] H. E. Nigh, S. Legvold, and F. H. Spedding, Physical Review 132, 1092 (1963)

  19. Rotating copper plasmoid in external magnetic field

    SciTech Connect

    Pandey, Pramod K.; Thareja, Raj K.

    2013-02-15

    Effect of nonuniform magnetic field on the expanding copper plasmoid in helium and argon gases using optical emission spectroscopy and fast imaging is presented. We report a peculiar oscillatory rotation of plasmoid in magnetic field and argon ambient. The temporal variation and appearance of the dip in the electron temperature show a direct evidence of the threading and expulsion of the magnetic field lines from the plasmoid. Rayleigh Taylor instability produced at the interface separating magnetic field and plasma is discussed.

  20. AC Magnetic Field Frequency Dependence of Magnetoacoustic Emission

    NASA Technical Reports Server (NTRS)

    Namkung, M.; Wincheski, B.; Fulton, J. P.; DeNale, R.

    1992-01-01

    Our recent study has proved a strong correlation between the low-frequency AC applied magnetic field amplitude dependence of the asymmetry of the magnetoacoustic emission (MAE) burst and the strength of the domain wall-defect interaction in iron-base ferromagnets. For the present study the AC magnetic field frequency dependence of the asymmetry has been investigated in the range of 1 to 200 Hz. When represented by the third moment of the rectified acoustic emission pulses, the asymmetry becomes a bell-shaped function of frequency with its center located around 25 Hz. This experiment has been performed with low carbon, high yield stress steel specimens of three different levels of domain wall-defect interaction strength. The results show that the increase in the interaction strength causes a vertical down shift of the asymmetry in the entire frequency range investigated.

  1. Sensorless operation of surface mount permanent magnet AC (PMAC) motors

    SciTech Connect

    Toliyat, H.A.; Rahman, K.M.; Shet, D.S.

    1999-12-01

    A sensorless field oriented control scheme for surface mount permanent magnet ac (PMAC) motor with split phase stator windings is presented. This motor is obtained by splitting the phase windings of a conventional three phase motor. The six-phase motor, however is run as a three-phase motor by connecting the split phase stator windings in series, while the taps are made available for voltage measurements. By measuring the terminal voltages and the line currents, absolute position of the permanent magnet ac motor driven by a current regulated PWM inverter with a hysteresis controller is estimated. The estimated position information is independent of the stator resistance, thus this scheme is even applicable at low speeds. Results are presented to show the effectiveness of the new controller, and it is also shown that the position error is negligible.

  2. Quark-gluon plasma in an external magnetic field.

    PubMed

    Levkova, L; DeTar, C

    2014-01-10

    Using numerical simulations of lattice QCD we calculate the effect of an external magnetic field on the equation of state of the quark-gluon plasma. The results are obtained using a Taylor expansion of the pressure with respect to the magnetic field for the first time. The coefficients of the expansion are computed to second order in the magnetic field. Our setup for the external magnetic field avoids complications arising from toroidal boundary conditions, making a Taylor series expansion straightforward. This study is exploratory and is meant to serve as a proof of principle. PMID:24483888

  3. A flux-coupled ac/dc magnetizing device

    NASA Astrophysics Data System (ADS)

    Gopman, D. B.; Liu, H.; Kent, A. D.

    2013-06-01

    We report on an instrument for applying ac and dc magnetic fields by capturing the flux from a rotating permanent magnet and projecting it between two adjustable pole pieces. This can be an alternative to standard electromagnets for experiments with small samples or in probe stations in which an applied magnetic field is needed locally, with advantages that include a compact form-factor, very low power requirements and dissipation as well as fast field sweep rates. This flux capture instrument (FLUXCAP) can produce fields from -400 to +400 mT, with field resolution less than 1 mT. It generates static magnetic fields as well as ramped fields, with ramping rates as high as 10 T/s. We demonstrate the use of this apparatus for studying the magnetotransport properties of spin-valve nanopillars, a nanoscale device that exhibits giant magnetoresistance.

  4. Hysteresis of sextupole and ac loss in Energy Doubler dipole magnets

    SciTech Connect

    Ishibashi, K.

    1982-06-18

    A simple model gave utilized for calculation of magnetization effects on ac loss and sextupole for Energy Doubler dipole magnets. The calculation in the simple model gave an underestimation of ac loss by about 30%. Results of computation on ac harmonics were also described.

  5. Floating and flying ferrofluid bridges induced by external magnetic fields

    NASA Astrophysics Data System (ADS)

    Ma, Rongchao; Zhou, Yixin; Liu, Jing

    2015-04-01

    A ferrofluid is a mixture that exhibits both magnetism and fluidity. This merit enables the ferrofluid to be used in a wide variety of areas. Here we show that a floating ferrofluid bridge can be induced between two separated boards under a balanced external magnetic field generated by two magnets, while a flying ferrofluid bridge can be induced under an unbalanced external magnetic field generated by only one magnet. The mechanisms of the ferrofluid bridges were discussed and the corresponding mathematical equations were also established to describe the interacting magnetic force between the ferro particles inside the ferrofluid. This work answered a basic question that, except for the well-known floating water bridges that are related to electricity, one can also build up a liquid bridge that is related to magnetism.

  6. Decay Characteristics of Levitation Force of YBCO Bulk Exposed to AC Magnetic Field above NdFeB Guideway

    NASA Astrophysics Data System (ADS)

    Liu, Minxian; Lu, Yiyun; Wang, Suyu; Ma, Guangtong

    2011-04-01

    The superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneity of the material property of the NdFeB magnet. So it is required to study the characteristics of levitation force of the bulks affected by the non-uniform applied magnetic fields along the moving direction. In this paper, we will study the characteristics of the levitation force relaxation between the HTS bulk and the NdFeB guideway by an experiment in which AC external magnetic field generated by an electromagnet is used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway. From the experimental results, it has found that the levitation force is decreasing with the application of the AC external magnetic field, and the decay increasing with the amplitude of the applied magnetic field and is almost independent of the frequency.

  7. Time-dependent meson melting in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Ali-Akbari, M.; Charmchi, F.; Davody, A.; Ebrahim, H.; Shahkarami, L.

    2015-05-01

    The dynamics of a probe D7-brane in an asymptotically anti-de Sitter-Vaidya background has been investigated in the presence of an external magnetic field. Holographically, this is dual to the dynamical meson melting in the N =2 super Yang-Mills theory. If the final temperature of the system is large enough, the probe D7-brane will dynamically cross the horizon (the black hole embedding). By turning on the external magnetic field and raising it sufficiently, the final embedding of the corresponding D7-brane changes to a Minkowski embedding. On the field theory side, this means that the mesons which melt due to the raise in the temperature will form bound states again by applying an external magnetic field. We also show that the evolution of the system to its final equilibrium state is postponed due to the presence of the magnetic field.

  8. Vortex activation energy in the AC magnetic response of superconducting YBa2Cu3O7 thin films with complex pinning structures

    NASA Astrophysics Data System (ADS)

    Ivan, I.; Ionescu, A. M.; Miu, D.; Mele, P.; Miu, L.

    2016-09-01

    The vortex activation energy U AC in the AC magnetic response of superconductors exhibits a logarithmic variation with the screening current density J (regardless of the pinning structure details), and takes surprisingly high values in the vicinity of the DC irreversibility line, especially at low external DC magnetic fields, as often reported. This is essentially different from the behaviour of the vortex-creep activation energy at long relaxation time scales in DC magnetic measurements, and is not completely understood. We investigated the DC relaxation and the AC response for YBa2Cu3O7 films containing nanorods and nanoparticles, with the DC and AC fields oriented perpendicular to the film surface. It is shown that the large U AC values in the vicinity of the DC irreversibility line, where the critical-state-related AC signal occurs, are generated by a non-diffusive vortex motion during the AC cycle, with the mean vortex hopping length longer than the average distance between the pinning centres. In these conditions, the smearing of the vortex pinning potential by thermally induced vortex fluctuations is weak, and U AC mainly results from the strong influence of the pinning-enhanced viscous drag on the vortex hopping process. The logarithmic U AC(J) dependence is consistent with a high U AC.

  9. A Prototype External Magnetic Eyelid Device for Blepharoptosis

    PubMed Central

    Houston, Kevin E.; Tomasi, Matteo; Yoon, Michael; Paschalis, Eleftherios I.

    2014-01-01

    Purpose To test a prototype magnet system (magnetic levator prosthesis) for the ability to comfortably and non-invasively provide eye opening with maintenance of the blink in people with paralytic ptosis and determine preliminary efficacy for short-term clinical application. Methods The prototype device consisted of a magnet on a spectacle frame and a micro-magnet array mounted externally on the eyelid. Participants with unilateral CN III palsy (n=3) trialed the predicate (ptosis crutch) and magnet device. Video analysis was used to quantify changes in eyelid opening and subjective responses were documented with a rating scale. A 20-minute and then a 1-week trial were offered. Results The magnetic levator prosthesis device was effective to provide eye opening while allowing, at minimum, a volitional blink without ill effects on the eyelid skin or ocular surface. Comfort scores ranged from 6 to 9 out of 10 over 3 evaluations. All patients chose an extended trial of the magnet device and reported continued 8-9/10 comfort and efficacy after the extended 1-week trial. Conclusions Comfortable and effective restoration of eye opening with maintenance of the blink is feasible using external static magnets and warrants further study. Translational Relevance This is the first careful documentation of the successful use of an externally mounted static magnet system to treat paralytic ptosis. PMID:25674358

  10. Neutrino dispersion in external magnetic fields

    SciTech Connect

    Kuznetsov, A. V.; Mikheev, N. V.; Vassilevskaya, L. A.; Raffelt, G. G.

    2006-01-15

    We calculate the neutrino self-energy operator {sigma}(p) in the presence of a magnetic field B. In particular, we consider the weak-field limit eB<magnetized plasma.

  11. Analysis of magnetic refrigerators with external regeneration

    SciTech Connect

    Overton, W.C. Jr.; Barclay, J.A.

    1986-01-01

    The central idea of the magnetic refrigeration systems analyzed in this paper is that of a MR having a regenerator composed of an integral number of separate stages but having only a single magnetic stage. In principle, each stage is thermally isolated from the others, but the stages are accessed by a manifold and valve system which allows gas to flow between the MM and the individual stages. The concept therefore is distinctly unlike that of the unusual continuous regenerator of gas refrigerators. Although a small amount of gas in the manifold is responsible for the actual transfer of heat between elements of the REGMR, it is clear from the cycle description in the caption of Fig. 1 that the fixed mass of the MM is analogous to a fixed mass of a working fluid in a gas refrigerator or engine. Both, in effect, are carried thermally through all parts of their respective systems.

  12. Enhancement of the thermoelectric figure of merit in a quantum dot due to external ac field

    NASA Astrophysics Data System (ADS)

    Chen, Qiao; Wang, Zhi-yong; Xie, Zhong-Xiang

    2013-08-01

    We investigate the figure of merit of a quantum dot (QD) system irradiated with an external microwave filed by nonequilibrium Green's function (NGF) technique. Results show that the frequency of microwave field influence the figure of merit ZT significantly. At low temperature, a sharp peak can be observed in the figure of merit ZT as the frequency of ac field increases. As the frequency varies, several zero points and resonant peaks emerge in the figure of merit ZT. By adjusting the frequency of the microwave field, we can obtain high ZT. The figure of merit ZT increases with the decreasing of linewidth function Γ. In addition, Wiedemann-Franz law does not hold, particularly in the low frequency region due to multi-photon emission and absorption. Some novel thermoelectric properties are also found in two-level QD system.

  13. New levitation scheme with AC superconducting magnet for EDS MAGLEV system

    SciTech Connect

    Kim, D.H.; Lee, J.K.; Hahn, S.Y.; Cha, G.

    1996-09-01

    This paper proposes a new magnetic levitation scheme which is able to generate levitation force for all speeds including a standstill. Auxiliary wheels which are needed in EDS MAGLEV vehicle can be eliminated. This scheme uses AC superconducting magnets to generate levitation force. In this paper, magnetic fields, forces and power dissipations generated by AC magnets moving above a conducting slab are calculated analytically. Results of calculation show characteristics of EDS system with AC magnet, such as levitation force and loss, are superior to those of EDS system with DC magnets for all speeds.

  14. ac susceptibility study of a magnetite magnetic fluid

    NASA Astrophysics Data System (ADS)

    Ayala-Valenzuela, O. E.; Matutes-Aquino, J. A.; Galindo, J. T. Elizalde; Botez, C. E.

    2009-04-01

    Magnetite nanometric powder was synthesized from metal salts using a coprecipitation technique. The powders were used to produce magnetic fluid via a peptization method, with hydrocarbon Isopar M as liquid carrier and oleic acid as surfactant. The complex magnetic susceptibility χ =χ'+iχ″ was measured as a function of temperature T in steps of 2.5 K from 3 to 298 K for frequencies ranging from f =10 to 10 000 Hz. The magnetic fluid real and imaginary components of the ac susceptibility show a prominent maximum at temperatures that increase with the measuring frequency, which is attributed to a spin-glass-like behavior. The peak temperature Tp1 of χ″ depends on f following the Vogel-Fulcher law f =f0 exp[E /kB(Tp1-T0)], where f0 and E are positive constants and T0 is a parameter related to particle interactions. There is another kind of peak temperature, Tp2, in the loss factor tan δ =χ″/χ' which is related to a magnetic aftereffect. The peak temperature Tp2 is far less than Tp1 and shows an Arrhenius-type dependence on f.

  15. Rapid magnetic microfluidic mixer utilizing AC electromagnetic field.

    PubMed

    Wen, Chih-Yung; Yeh, Cheng-Peng; Tsai, Chien-Hsiung; Fu, Lung-Ming

    2009-12-01

    This paper presents a novel simple micromixer based on stable water suspensions of magnetic nanoparticles (i.e. ferrofluids). The micromixer chip is built using standard microfabrication and simple soft lithography, and the design can be incorporated as a subsystem into any chemical microreactor or a miniaturized biological sensor. An electromagnet driven by an AC power source is used to induce transient interactive flows between a ferrofluid and Rhodamine B. The alternative magnetic field causes the ferrofluid to expand significantly and uniformly toward Rhodamine B, associated with a great number of extremely fine fingering structures on the interface in the upstream and downstream regions of the microchannel. These pronounced fingering patterns, which have not been observed by other active mixing methods utilizing only magnetic force, increase the mixing interfacial length dramatically. Along with the dominant diffusion effects occurring around the circumferential regions of the fine finger structures, the mixing efficiency increases significantly. The miscible fingering instabilities are observed and applied in the microfluidics for the first time. This work is carried with a view to developing functionalized ferrofluids that can be used as sensitive pathogen detectors and the present experimental results demonstrate that the proposed micromixer has excellent mixing capabilities. The mixing efficiency can be as high as 95% within 2.0 s and a distance of 3.0 mm from the inlet of the mixing channel, when the applied peak magnetic field is higher than 29.2 Oe and frequency ranges from 45 to 300 Hz. PMID:19921677

  16. Ac magnetorestriction hysteresis and magnetization direction in grain oriented silicon steels

    SciTech Connect

    Mogi, Hisashi; Matsuo, Yukio; Kumano, Tomoji

    1999-09-01

    A hysteresis curve of ac magnetostriction was measured, magnetizing a grain oriented silicon steel in the direction deviated from rolling direction of a sample. The ac magnetostriction ({lambda} ac) curves were analyzed as harmonics in the interest of noise spectrum of such as a power transformer. The domain structure model in this magnetostriction process was proposed. The hysteresis was large in the magnetization direction inclined at 30 and 90{degree} from the rolling direction.

  17. AC magnetic field losses in BSCCO-2223 superconducting tapes

    SciTech Connect

    Lelovic, M.; Mench, S.; Deis, T.

    1997-09-01

    The AC magnetic losses at power frequencies (60 Hz) were investigated for mono- and multifilament Ag-sheathed (Bi, Pb){sub 2}Sr{sub 2}Ca{sub 2}Cu{sub 3}O{sub y} (BSCCO-2223) tapes with similar transport critical current (I{sub c}) values at 77 K. The multifilament sample exhibited higher losses than the monofilament under the same conditions. Loss peaks are discussed in terms of intergranular, intragranular and eddy current losses. Because of BSCCO`s anisotropy, field orientation has a large effect on the magnitude of these peaks, even at relatively small angles. Losses for fields applied parallel to the c-axis of the textured BSCCO grains are larger by more than one order of magnitude than those applied perpendicular.

  18. Spectroscopic AC susceptibility imaging (sASI) of magnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Ficko, Bradley W.; Nadar, Priyanka M.; Diamond, Solomon G.

    2015-02-01

    This study demonstrates a method for alternating current (AC) susceptibility imaging (ASI) of magnetic nanoparticles (mNPs) using low cost instrumentation. The ASI method uses AC magnetic susceptibility measurements to create tomographic images using an array of drive coils, compensation coils and fluxgate magnetometers. Using a spectroscopic approach in conjunction with ASI, a series of tomographic images can be created for each frequency measurement set and is termed sASI. The advantage of sASI is that mNPs can be simultaneously characterized and imaged in a biological medium. System calibration was performed by fitting the in-phase and out-of-phase susceptibility measurements of an mNP sample with a hydrodynamic diameter of 100 nm to a Brownian relaxation model (R2=0.96). Samples of mNPs with core diameters of 10 and 40 nm and a sample of 100 nm hydrodynamic diameter were prepared in 0.5 ml tubes. Three mNP samples were arranged in a randomized array and then scanned using sASI with six frequencies between 425 and 925 Hz. The sASI scans showed the location and quantity of the mNP samples (R2=0.97). Biological compatibility of the sASI method was demonstrated by scanning mNPs that were injected into a pork sausage. The mNP response in the biological medium was found to correlate with a calibration sample (R2=0.97, p<0.001). These results demonstrate the concept of ASI and advantages of sASI.

  19. Spectroscopic AC Susceptibility Imaging (sASI) of Magnetic Nanoparticles

    PubMed Central

    Ficko, Bradley W.; Nadar, Priyanka M.; Diamond, Solomon G.

    2014-01-01

    This study demonstrates a method for alternating current (AC) susceptibility imaging (ASI) of magnetic nanoparticles (mNPs) using low cost instrumentation. The ASI method uses AC magnetic susceptibility measurement to create tomographic images using an array of drive coils, compensation coils and fluxgate magnetometers. Using a spectroscopic approach in conjunction with ASI, a series of tomographic images can be created for each frequency measurement and is termed sASI. The advantage of sASI is that mNPs can be simultaneously characterized and imaged in a biological medium. System calibration was performed by fitting the in-phase and out-of-phase susceptibility measurements of an mNP sample with a hydrodynamic diameter of 100 nm to a Brownian relaxation model (R2 = 0.96). Samples of mNPs with core diameters of 10 and 40 nm and a sample of 100 nm hydrodynamic diameter were prepared in 0.5 ml tubes. Three mNP samples were arranged in a randomized array and then scanned using sASI with six frequencies between 425 and 925 Hz. The sASI scans showed the location and quantity of the mNP samples (R2 = 0.97). Biological compatibility of the sASI method was demonstrated by scanning mNPs that were injected into a pork sausage. The mNP response in the biological medium was found to correlate with a calibration sample (R2 = 0.97, p <0.001). These results demonstrate the concept of ASI and advantages of sASI. PMID:25477704

  20. Spectroscopic AC Susceptibility Imaging (sASI) of Magnetic Nanoparticles.

    PubMed

    Ficko, Bradley W; Nadar, Priyanka M; Diamond, Solomon G

    2015-02-01

    This study demonstrates a method for alternating current (AC) susceptibility imaging (ASI) of magnetic nanoparticles (mNPs) using low cost instrumentation. The ASI method uses AC magnetic susceptibility measurement to create tomographic images using an array of drive coils, compensation coils and fluxgate magnetometers. Using a spectroscopic approach in conjunction with ASI, a series of tomographic images can be created for each frequency measurement and is termed sASI. The advantage of sASI is that mNPs can be simultaneously characterized and imaged in a biological medium. System calibration was performed by fitting the in-phase and out-of-phase susceptibility measurements of an mNP sample with a hydrodynamic diameter of 100 nm to a Brownian relaxation model (R(2) = 0.96). Samples of mNPs with core diameters of 10 and 40 nm and a sample of 100 nm hydrodynamic diameter were prepared in 0.5 ml tubes. Three mNP samples were arranged in a randomized array and then scanned using sASI with six frequencies between 425 and 925 Hz. The sASI scans showed the location and quantity of the mNP samples (R(2) = 0.97). Biological compatibility of the sASI method was demonstrated by scanning mNPs that were injected into a pork sausage. The mNP response in the biological medium was found to correlate with a calibration sample (R(2) = 0.97, p <0.001). These results demonstrate the concept of ASI and advantages of sASI. PMID:25477704

  1. Computing the External Magnetic Scalar Potential due to an Unbalanced Six-Pole Permanent Magnet Motor

    SciTech Connect

    Selvaggi J, Salon S, Kwon O, Chari MVK

    2007-02-12

    The accurate computation of the external magnetic field from a permanent magnet motor is accomplished by first computing its magnetic scalar potential. In order to find a solution which is valid for any arbitrary point external to the motor, a number of proven methods have been employed. Firstly, A finite element model is developed which helps generate magnetic scalar potential values valid for points close to and outside the motor. Secondly, charge simulation is employed which generates an equivalent magnetic charge matrix. Finally, an equivalent multipole expansion is developed through the application of a toroidal harmonic expansion. This expansion yields the harmonic components of the external magnetic scalar potential which can be used to compute the magnetic field at any point outside the motor.

  2. AC magnetic measurements of the ALS Booster Dipole Engineering Model Magnet

    SciTech Connect

    Green, M.I.; Keller, R.; Nelson, D.H.; Hoyer, E.

    1989-03-01

    10 Hz sine wave and 2 Hz sawtooth AC magnetic measurements of he curved ALS Booster Dipole Engineering Model Magnet have been accomplished. Long curved coils were utilized to measure the integral transfer function and uniformity. Point coils and a Hall Probe were used to measure magnetic induction and its uniformity. The data were logged and processed by a Tektronix 11401 digital oscilloscope. The dependence of the effective length on the field was determined from the ratio of the integral coil signals to the point coil signals. Quadrupole and sextupole harmonics were derived from the point and integral uniformity measurements. 5 refs., 4 figs., 2 tabs.

  3. Calorimetric AC loss measurement of MgB2 superconducting tape in an alternating transport current and direct magnetic field

    NASA Astrophysics Data System (ADS)

    See, K. W.; Xu, X.; Horvat, J.; Cook, C. D.; Dou, S. X.

    2012-11-01

    Applications of MgB2 superconductors in electrical engineering have been widely reported, and various studies have been made to define their alternating current (AC) losses. However, studies on the transport losses with an applied transverse DC magnetic field have not been conducted, even though this is one of the favored conditions in applications of practical MgB2 tapes. Methods and techniques used to characterize and measure these losses have so far been grouped into ‘electrical’ and ‘calorimetric’ approaches with external conditions set to resemble the application conditions. In this paper, we present a new approach to mounting the sample and employ the calorimetric method to accurately determine the losses in the concurrent application of AC transport current and DC magnetic fields that are likely to be experienced in practical devices such as generators and motors. This technique provides great simplification compared to the pickup coil and lock-in amplifier methods and is applied to a long length (˜10 cm) superconducting tape. The AC loss data at 20 and 30 K will be presented in an applied transport current of 50 Hz under external DC magnetic fields. The results are found to be higher than the theoretical predictions because of the metallic fraction of the tape that contributes quite significantly to the total losses. The data, however, will allow minimization of losses in practical MgB2 coils and will be used in the verification of numerical coil models.

  4. Thermomagnetism with external and internal magnetic field quantities

    NASA Astrophysics Data System (ADS)

    Egolf, Peter W.; Gama, Sergio; Vuarnoz, Didier

    2015-07-01

    In magnetism literature, usually the applied or external field H0 is taken to present the results of an investigation. But for certain purposes, it is advantageous to work with the internal magnetic field H that occurs inside a magnetic body. It is well-known that the susceptibility of the material and the demagnetization effect, given by the geometry of a body, link the two usually different fields under consideration. If a probe is a long needle with the external magnetic field and the magnetization in the probe parallel to the axis of the slender body, the two fields are identical. But when building thermomagnetic machines, other demands may require also other shapes (porous materials, particle beds, wavy structures, etc.) of the magnetized material and then a correct distinction of these fields becomes important and in some cases also laborious if one of them must be theoretically determined from the other. This article shows how—from a theoretical point of view—the most important physical properties of thermomagnetism/magnetocalorics, namely, the adiabatic entropy change, the effective specific heat capacity, and the adiabatic temperature change must be transformed. Furthermore, this theory reveals the invariants of magnetocalorics, which are combinations of these three most important properties.

  5. External Electromagnetic Fields of Slowly Rotating Relativistic Magnetized NUT Stars

    NASA Astrophysics Data System (ADS)

    Ahmedov, B. J.; Khugaev, A. V.

    2006-08-01

    Analytic general relativistic expressions for the electromagnetic fields external to a slowly-rotating magnetized NUT star with non-vanishing gravitomagnetic charge have been presented. Solutions for the electric and magnetic fields have been found after separating the Maxwell equations in the external background spacetime of a slowly rotating NUT star into angular and radial parts in the lowest order approximation in specific angular momentum and NUT parameter . The relativistic star is considered isolated and in vacuum, with different models for stellar magnetic field: i) monopolar magnetic field and ii) dipolar magnetic field aligned with the axis of rotation. It has been shown that the general relativistic corrections due to the dragging of reference frames and gravitomagnetic charge are not present in the form of the magnetic fields but emerge only in the form of the electric fields. In particular, it has been obtained that the frame-dragging and gravitomagnetic charge provide an additional induced electric field which is analogous to the one introduced by the rotation of the star in the flat spacetime limit.

  6. Temperature Dependence of AC Magnetic Properties of FeCo-Based Soft Magnetic Alloys

    NASA Astrophysics Data System (ADS)

    Xiao, J. Q.; Yu, R. H.; Basu, S.

    1998-03-01

    AC magnetic properties of soft FeCo-based alloys have been studied at different temperatures and frequencies. Samples of Fe_49Co_49V2 (Hiperco50), Fe_49Co_49V_1.7Nb_0.3 (Hiperco 50HS), and Fe_72Co_27Cr_0.5Mn_0.5 (Hiperco 27) were selected and heat-treated to obtain different microstructures. TEM observation reveals that the ordering parameter of the BCC phase in Hiperco 50 series vary with the cooling rate, and a high temperature disordered phase with a high density of defects can be retained through rapid quenching, whereas Hiperco 27 exhibits a disordered structure which is insensitive to the heat treatment. Toroidal laminated samples were used to measure AC magnetic properties. At low frequencies, all the samples either with ordered or disordered phases show low coercivity H_c, high magnetization and initial permeability μ. As the frequency increases, Hc increases and μ decreases due to the damping effect of the magnetic domain walls. In a certain range of frequencies, magnetic permeability spectra show a dispersion zone where the permeability sharply decreases near to zero. This magnetic permeability dispersion zone shifts to lower frequencies with increasing temperature and decreasing ordering parameter. The effect of microstructure, frequency and temperature on core losses will be also presented.

  7. Dynamics of molecular superrotors in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Korobenko, Aleksey; Milner, Valery

    2015-08-01

    We excite diatomic oxygen and nitrogen to high rotational states with an optical centrifuge and study their dynamics in an external magnetic field. Ion imaging is employed to directly visualize, and follow in time, the rotation plane of the molecular superrotors. The two different mechanisms of interaction between the magnetic field and the molecular angular momentum in paramagnetic oxygen and non-magnetic nitrogen lead to qualitatively different behaviour. In nitrogen, we observe the precession of the molecular angular momentum around the field vector. In oxygen, strong spin-rotation coupling results in faster and richer dynamics, encompassing the splitting of the rotation plane into three separate components. As the centrifuged molecules evolve with no significant dispersion of the molecular wave function, the observed magnetic interaction presents an efficient mechanism for controlling the plane of molecular rotation.

  8. Spherical shock in the presence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    Kuramitsu, Y.; Matsukiyo, S.; Isayama, S.; Harada, D.; Oyama, T.; Fujino, R.; Sakawa, Y.; Morita, T.; Yamaura, Y.; Ishikawa, T.; Moritaka, T.; Sano, T.; Tomita, K.; Shimoda, R.; Sato, Y.; Uchino, K.; Pelka, A.; Crowston, R.; Woolsey, N.; Gregori, G.; Koenig, M.; Yuan, D. W.; Yin, C. L.; Li, Y. T.; Zhang, K.; Zhong, J. Y.; Wang, F. L.; Ohnishi, N.; Nagamine, K.; Yoneda, H.; Takabe, H.

    2016-03-01

    We investigate spherical collisionless shocks in the presence of an external magnetic field. Spherical collisionless shocks are common resultant of interactions between a expanding plasma and a surrounding plasma, such as the solar wind, stellar winds, and supernova remnants. Anisotropies often observed in shock propagations and their emissions, and it is widely believed a magnetic field plays a major role. Since the local observations of magnetic fields in astrophysical plasmas are not accessible, laboratory experiments provide unique capability to investigate such phenomena. We model the spherical shocks in the universe by irradiating a solid spherical target surrounded by a plasma in the presence of a magnetic field. We present preliminary results obtained by shadowgraphy.

  9. Enhancement of fast electron energy deposition by external magnetic fields

    NASA Astrophysics Data System (ADS)

    Honrubia, J. J.; Murakami, M.; Mima, K.; Johzaki, T.; Sunahara, A.; Nagatomo, H.; Fujioka, S.; Shiraga, H.; Azechi, H.

    2016-03-01

    Recently, generation of external magnetic fields of a few kT has been reported [Fujioka et al. Scientific Reports 2013 3 1170]. These fields can be used in fast ignition to mitigate the large fast electron divergence. In this summary, two fast ignition applications are briefly outlined. The first one deals with electron guiding by external B-fields applied at the end of the shell implosion of a re-entrant cone target. Preliminary results show that the B-field strength at the time of peak ρR may be sufficiently high for fast electron guiding. The second application deals with guiding of fast electrons in magnetized wires surrounded by plasma. Results show a significant enhancement of electron energy deposition at the end of the wire, which is particularly important for low-Z wires.

  10. Influence of Critical Current Density on Guidance Force Decay of HTS Bulk Exposed to AC Magnetic Field Perturbation in a Maglev Vehicle System

    NASA Astrophysics Data System (ADS)

    Longcai, Zhang; Jianguo, Kong

    2012-07-01

    Superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the HTS bulks are always exposed to AC external magnetic field, which is generated by the inhomogeneous surface magnetic field of the NdFeB guideway. In our previous work, we studied the guidance force decay of the YBCO bulk over the NdFdB guideway used in the High-temperature superconducting maglev vehicle system with the application of the AC external magnetic field, and calculated the guidance force decay as a function of time based on an analytic model. In this paper, we investigated the influence of the critical current density on the guidance force decay of HTS bulk exposed to AC field perturbation in the maglev vehicle system and try to adopt a method to suppress the decay. From the results, it was found that the guidance force decay rate was higher for the bulk with lower critical current density. Therefore, we could suppress the guidance force decay of HTS bulk exposed to AC external magnetic field perturbation in the maglev vehicle system by improving critical current density of the bulk.

  11. Synthesis of Ultralong Polyaniline Nanorods by Magnetic Nanoparticles as Templates Under External Magnetic Field.

    PubMed

    Miao, Tingting; Li, Yijing; Zhang, Dongmei

    2016-06-01

    We report the successful synthesis of ultralong polyaniline nanorods (UL-PANI-NRs) via using water-soluble magnetic Fe3O4 nanoparticles as soft templates under the assistance of external magnetic field. It was found that the concentration of Fe3O4 nanoparticles, the aniline concentration and the use of an external magnetic field significantly affect the morphology of the PANI products. The following characterizations including transmission electron microscopy (TEM), Fourier-Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD). and thermogravimetric analysis (TGA) were conducted to investigate the electronic structure and composition of as-prepared UL-PANI-NRs. Our preliminary result indicates that complicated polymer structures (such as ultralong rods with vertical branches) may be prepared by water-soluble magnetic Fe3O4 nanoparticles as soft templates under the assistance of alternatively external magnetic fields. PMID:27427623

  12. Anisotropy of 2G HTS racetrack coils in external magnetic fields

    NASA Astrophysics Data System (ADS)

    Chudy, Michal; Chen, Yiran; Zhang, Min; Coombs, T. A.

    2013-07-01

    Pancake or racetrack coils wound with second generation high-temperature superconductors (2G HTSs) are important elements for numerous applications of HTS. The applications of these coils are primarily in rotating machines such as motors and generators where they must withstand external magnetic fields from various orientations. The characterization of 2G HTS coils is mostly focused on AC loss assessment, critical current and maximum magnetic field evaluation. In this study, racetrack coils will be placed in different orientations of external magnetic fields—Jc (Ic) versus angle measurements will be performed and interpreted. Full attention is paid to studies of anisotropy Jc versus angle curves for short samples of 2G HTS tapes. As will be shown, the shape of the Jc versus angle curves for tapes has a strong influence on the Jc (Ic) versus angle curves for coils. In this work, a unique and unpredicted behavior of the Jc versus angle curves for the 2G HTS racetrack coils was found. This will be analyzed and fully explained.

  13. Anisotropic magnetohydrodynamic turbulence in a strong external magnetic field

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Turner, L.

    1981-01-01

    A strong external dc magnetic field introduces a basic anisotropy in incompressible MHD turbulence. The modifications that this is likely to produce in the properties of the turbulence are investigated for high Reynolds numbers. It is found that the turbulent spectrum splits into two parts: (1) an essentially two-dimensional spectrum with both the velocity field and the magnetic fluctuations perpendicular to the dc magnetic field, and (2) a generally weaker and more nearly isotropic spectrum of Alfven waves. These results are discussed in relation to measurements from the Culham-Harwell Zeta pinch device and the UCLA Macrorotor tokamak, as well as in relation to measurements of MHD turbulence in the solar wind.

  14. Anisotropic magnetohydrodynamic turbulence in a strong external magnetic field

    NASA Technical Reports Server (NTRS)

    Montgomery, D.; Turner, L.

    1981-01-01

    A strong external dc magnetic field introduces a basic anisotropy into incompressible magnetohydrodynamic turbulence. The modifications that this is likely to produce in the properties of the turbulence are explored for the high Reynolds number case. The conclusion is reached that the turbulent spectrum splits into two parts: an essentially two dimensional spectrum with both the velocity field and magnetic fluctuations perpendicular to the dc magnetic field, and a generally weaker and more nearly isotropic spectrum of Alfven waves. A minimal characterization of the spectral density tensors is given. Similarities to measurements from the Culham-Harwell Zeta pinch device and the UCLA Macrotor Tokamak are remarked upon, as are certain implications for the Belcher and Davis measurements of magnetohydrodynamic turbulence in the solar wind.

  15. A magnetic minirobot with anchoring and drilling ability in tubular environments actuated by external magnetic fields

    NASA Astrophysics Data System (ADS)

    Choi, K.; Jeon, S. M.; Nam, J. K.; Jang, G. H.

    2015-05-01

    We propose a magnetic minirobot with anchoring and drilling ability (MMAD) controlled by an external magnetic field. The proposed MMAD can navigate through a tubular environment, such as human blood vessels, actuated by a magnetic gradient and uniform rotating magnetic field. It can also generate an anchoring motion, which stably holds the position of the MMAD under pulsatile flow, in order to drill and unclog obstructed blood vessels. The operating conditions of the MMAD were examined by investigating the magnetic torques, and the holding force of the MMAD was measured by a force sensing resistor. Finally, we performed various experiments in a tubular environment to verify the validity of the proposed MMAD.

  16. Decadal period external magnetic field variations determined via eigenanalysis

    NASA Astrophysics Data System (ADS)

    Shore, R. M.; Whaler, K. A.; Macmillan, S.; Beggan, C.; Velímský, J.; Olsen, N.

    2016-06-01

    We perform a reanalysis of hourly mean magnetic data from ground-based observatories spanning 1997-2009 inclusive, in order to isolate (after removal of core and crustal field estimates) the spatiotemporal morphology of the external fields important to mantle induction, on (long) periods of months to a full solar cycle. Our analysis focuses on geomagnetically quiet days and middle to low latitudes. We use the climatological eigenanalysis technique called empirical orthogonal functions (EOFs), which allows us to identify discrete spatiotemporal patterns with no a priori specification of their geometry -- the form of the decomposition is controlled by the data. We apply a spherical harmonic analysis to the EOF outputs in a joint inversion for internal and external coefficients. The results justify our assumption that the EOF procedure responds primarily to the long-period external inducing field contributions. Though we cannot determine uniquely the contributory source regions of these inducing fields, we find that they have distinct temporal characteristics which enable some inference of sources. An identified annual-period pattern appears to stem from a north-south seasonal motion of the background mean external field distribution. Separate patterns of semiannual and solar-cycle-length periods appear to stem from the amplitude modulations of spatially fixed background fields.

  17. Magnetic images of the disintegration process of tablets in the human stomach by ac biosusceptometry

    NASA Astrophysics Data System (ADS)

    Corá, L. A.; Andreis, U.; Romeiro, F. G.; Américo, M. F.; Oliveira, R. B.; Baffa, O.; Miranda, J. R. A.

    2005-12-01

    Oral administration of solid dosage forms is usually preferred in drug therapy. Conventional imaging methods are essential tools to investigate the in vivo performance of these formulations. The non-invasive technique of ac biosusceptometry has been introduced as an alternative in studies focusing on gastrointestinal motility and, more recently, to evaluate the behaviour of magnetic tablets in vivo. The aim of this work was to employ a multisensor ac biosusceptometer system to obtain magnetic images of disintegration of tablets in vitro and in the human stomach. The results showed that the transition between the magnetic marker and the magnetic tracer characterized the onset of disintegration (t50) and occurred in a short time interval (1.1 ± 0.4 min). The multisensor ac biosusceptometer was reliable to monitor and analyse the in vivo performance of magnetic tablets showing accuracy to quantify disintegration through the magnetic images and to characterize the profile of this process.

  18. AC loss measurement of superconducting dipole magnets by the calorimetric method

    SciTech Connect

    Morita, Y.; Hara, K.; Higashi, N.; Kabe, A.

    1996-12-31

    AC losses of superconducting dipole magnets were measured by the calorimetric method. The magnets were model dipole magnets designed for the SSC. These were fabricated at KEK with 50-mm aperture and 1.3-m overall length. The magnet was set in a helium cryostat and cooled down to 1.8 K with 130 L of pressurized superfluid helium. Heat dissipated by the magnet during ramp cycles was measured by temperature rise of the superfluid helium. Heat leakage into the helium cryostat was 1.6 W and was subtracted from the measured heat to obtain AC loss of the magnet. An electrical measurement was carried out for calibration. Results of the two methods agreed within the experimental accuracy. The authors present the helium cryostat and measurement system in detail, and discuss the results of AC loss measurement.

  19. A reentrant phenomenon in magnetic and dielectric properties of Dy2BaNiO5 and an intriguing influence of external magnetic field.

    PubMed

    Basu, Tathamay; Paulose, P L; Iyer, K K; Singh, K; Mohapatra, N; Chowki, S; Gonde, B; Sampathkumaran, E V

    2014-04-30

    We report that the spin-chain compound Dy2BaNiO5, recently proven by us to exhibit magnetoelectric coupling below its Néel temperature (TN) of 58 K, exhibits strong frequency-dependent behavior in ac magnetic susceptibility and complex dielectric properties at low temperatures (<10 K), mimicking the 'reentrant' multiglass phenomenon. Such a behavior is not known among undoped compounds. A new finding in the field of multiferroics is that the characteristic magnetic feature at low temperatures moves towards higher temperatures in the presence of a magnetic field (H), whereas the corresponding dielectric feature shifts towards lower temperatures with H, unlike the situation near TN. This observation indicates that the alignment of spins by external magnetic fields tends to inhibit glassy-like slow electric-dipole dynamics, at least in this system, possibly arising from peculiarities in the magnetic structure. PMID:24722401

  20. Relativistic Killingbeck energy states under external magnetic fields

    NASA Astrophysics Data System (ADS)

    Eshghi, M.; Mehraban, H.; Ikhdair, S. M.

    2016-07-01

    We address the behavior of the Dirac equation with the Killingbeck radial potential including the external magnetic and Aharonov-Bohm (AB) flux fields. The spin and pseudo-spin symmetries are considered. The correct bound state spectra and their corresponding wave functions are obtained. We seek such a solution using the biconfluent Heun's differential equation method. Further, we give some of our results at the end of this study. Our final results can be reduced to their non-relativistic forms by simply using some appropriate transformations. The spectra, in the spin and pseudo-spin symmetries, are very similar with a slight difference in energy spacing between different states.

  1. Controlling the dark exciton spin eigenstates by external magnetic field

    NASA Astrophysics Data System (ADS)

    Gantz, L.; Schmidgall, E. R.; Schwartz, I.; Don, Y.; Waks, E.; Bahir, G.; Gershoni, D.

    2016-07-01

    We study the dark exciton's behavior as a coherent physical two-level spin system (qubit) using an external magnetic field in the Faraday configuration. Our studies are based on polarization-sensitive intensity autocorrelation measurements of the optical transition resulting from the recombination of a spin-blockaded biexciton state, which heralds the dark exciton and its spin state. We demonstrate control over the dark exciton eigenstates without degrading its decoherence time. Our observations agree well with computational predictions based on a master equation model.

  2. Magnetic fluid hyperthermia (MFH): Cancer treatment with AC magnetic field induced excitation of biocompatible superparamagnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Jordan, Andreas; Scholz, Regina; Wust, Peter; Fähling, Horst; Felix, Roland

    1999-07-01

    The story of hyperthermia with small particles in AC magnetic fields started in the late 1950s, but most of the studies were unfortunately conducted with inadequate animal systems, inexact thermometry and poor AC magnetic field parameters, so that any clinical implication was far behind the horizon. More than three decades later, it was found, that colloidal dispersions of superparamagnetic (subdomain) iron oxide nanoparticles exhibit an extraordinary specific absorption rate (SAR [ W/ g]), which is much higher at clinically tolerable H 0 f combinations in comparison to hysteresis heating of larger multidomain particles. This was the renaissance of a cancer treatment method, which has gained more and more attention in the last few years. Due to the increasing number of randomized clinical trials preferentially in Europe with conventional E-field hyperthermia systems, the general medical and physical experience in hyperthermia application is also rapidly growing. Taking this increasing clinical experience carefully into account together with the huge amount of new biological data on heat response of cells and tissues, the approach of magnetic fluid hyperthermia (MFH) is nowadays more promising than ever before. The present contribution reviews the current state of the art and some of the future perspectives supported by advanced methods of the so-called nanotechnology.

  3. Brushed permanent magnet DC MLC motor operation in an external magnetic field

    SciTech Connect

    Yun, J.; St Aubin, J.; Rathee, S.; Fallone, B. G.

    2010-05-15

    Purpose: Linac-MR systems for real-time image-guided radiotherapy will utilize the multileaf collimators (MLCs) to perform conformal radiotherapy and tumor tracking. The MLCs would be exposed to the external fringe magnetic fields of the linac-MR hybrid systems. Therefore, an experimental investigation of the effect of an external magnetic field on the brushed permanent magnet DC motors used in some MLC systems was performed. Methods: The changes in motor speed and current were measured for varying external magnetic field strengths up to 2000 G generated by an EEV electromagnet. These changes in motor characteristics were measured for three orientations of the motor in the external magnetic field, mimicking changes in motor orientations due to installation and/or collimator rotations. In addition, the functionality of the associated magnetic motor encoder was tested. The tested motors are used with the Varian 120 leaf Millennium MLC (Maxon Motor half leaf and full leaf motors) and the Varian 52 leaf MKII MLC (MicroMo Electronics leaf motor) including a carriage motor (MicroMo Electronics). Results: In most cases, the magnetic encoder of the motors failed prior to any damage to the gearbox or the permanent magnet motor itself. This sets an upper limit of the external magnetic field strength on the motor function. The measured limits of the external magnetic fields were found to vary by the motor type. The leaf motor used with a Varian 52 leaf MKII MLC system tolerated up to 450{+-}10 G. The carriage motor tolerated up to 2000{+-}10 G field. The motors used with the Varian 120 leaf Millennium MLC system were found to tolerate a maximum of 600{+-}10 G. Conclusions: The current Varian MLC system motors can be used for real-time image-guided radiotherapy coupled to a linac-MR system, provided the fringe magnetic fields at their locations are below the determined tolerance levels. With the fringe magnetic fields of linac-MR systems expected to be larger than the

  4. Direction detectable static magnetic field imaging by frequency-modulated magnetic force microscopy with an AC magnetic field driven soft magnetic tip

    NASA Astrophysics Data System (ADS)

    Saito, Hitoshi; Ito, Ryoichi; Egawa, Genta; Li, Zhenghua; Yoshimura, Satoru

    2011-04-01

    Direction detectable static magnetic field imaging, which directly distinguishes the up and down direction of static perpendicular magnetic field from a sample surface and the polarity of magnetic charges on the surface, was demonstrated for CoCrPt-SiO2 perpendicular magnetic recording media based on a frequency-modulated magnetic force microscopy (FM-MFM), which uses a frequency modulation of the cantilever oscillation induced by an alternating force from the tip-sample magnetic interaction. In this study, to generate the alternating force, we used a NiFe soft magnetic tip driven by the ac magnetic field of a soft ferrite core and imaged the direction and the amplitude of the static magnetic field from the recorded bits. This method enables measurement of the static magnetic field near a sample surface, which is masked by short range forces of the surface. The present method will be effective in analyzing the microscopic magnetic domain structure of hard magnetic samples.

  5. Stability improvement of AC superconducting magnet by forced-convection cooling

    SciTech Connect

    Ishigohka, T.; Kasuya, A.; Ninomiya, A.

    1996-07-01

    The authors propose a new improved cooling system of an AC(50/60Hz) superconducting magnet introducing a forced-convection flow of liquid helium. In this system, the flow through the cooling channel between the winding layers is generated by a screw rotating in a cylinder surrounding the magnet. A small experimental device composed of an AC superconducting magnet and a rotating screw was manufactured. The screw was rotated by an extended driving shaft. The experimental result shows that the stability of the magnet is improved by the rotation of the screw. That is, the thermal disturbance (heater input power) which generates the quench of the magnet increases as the rotational speed of the screw does. It is expected that this technique can be successfully applied to superconducting AC power apparatuses as transformers or reactors.

  6. Depinning of flux lines and AC losses in magnet-superconductor levitation system

    SciTech Connect

    Terentiev, A. N.; Hull, J. R.; De Long, L. E.

    1999-11-29

    The AC loss characteristics of a magnet-superconductor system were studied with the magnet fixed to the free end of an oscillating cantilever located near a stationary melt-textured YBCO pellet. Below a threshold AC field amplitude {approx}2Oe, the dissipation of the oscillator is amplitude-independent, characteristic of a linear, non-hysteretic regime. Above threshold,dissipation increases with amplitude, reflecting the depinning and hysteretic motion of flux lines. The threshold AC field is an order of magnitude higher than that measured for the same YBCO material via AC susceptometry in a uniform DC magnetic field, A partial lock-in of flux lines between YBCO ab planes is proposed as the mechanism for the substantial increase of the depinning threshold.

  7. Study of effect of AC and DC magnetic fields on growth of Pisum sativum seeds

    NASA Astrophysics Data System (ADS)

    Bahar, Mahmood; Yasaie Mehrjardi, Yasaman; Sojoodi, Jaleh; Bayani, Hosien; Kazem Salem, Mohammad

    2013-08-01

    This paper concentrates on the effect of the AC and DC magnetic fields on plant growth. The effect of AC magnetic field with intensities of 2.25, 1.66 and 1.49 mT and DC magnetic field with intensities of 3.6, 2.41 and 2.05 mT in exposure durations of 2, 4, 6, 8, 10 and 12 min on two groups of dry and wet Pisum sativum seedlings was studied. In each experiment 10 seeds were used; the experiments were repeated three times for each group and there was a sham exposed group for comparison purposes. The light cycle was 12 h light/12 h darkness and the temperature was 25 ± 1° C. The index of growth is considered to be the root and stem elongation on the sixth day. It was observed that AC magnetic field has a positive effect on the growth in all durations and intensities. Moreover, it is highlighted that during the experiments, the mean growth of dry seedlings significantly increased by a factor of 11 in AC magnetic field with the lowest intensity of 1.49 mT (p < 0.05). It was also shown that AC magnetic fields had a more positive effect on the growth of plants in comparison to DC magnetic fields.

  8. Effects of sweep rates of external magnetic fields on the labyrinthine instabilities of miscible magnetic fluids

    NASA Astrophysics Data System (ADS)

    Wen, C.-Y.; Lin, J.-Z.; Chen, M.-Y.; Chen, L.-Q.; Liang, T.-K.

    2011-05-01

    The interfacial instability of miscible magnetic fluids in a Hele-Shaw Cell is studied experimentally, with different magnitudes and sweep rates of the external magnetic field. The initial circular oil-based magnetic fluid drop is surrounded by the miscible fluid, diesel. The external uniform magnetic fields induce small fingerings around the initial circular interface, so call labyrinthine fingering instability, and secondary waves. When the magnetic field is applied at a given sweep rate, the interfacial length grows significantly at the early stage. It then decreases when the magnetic field reaches the preset values, and finally approaches a certain asymptotic value. In addition, a dimensionless parameter, Pe, which includes the factors of diffusion and sweep rate of the external magnetic field, is found to correlate the experimental data. It is shown that the initial growth rate of the interfacial length is linearly proportional to Pe for the current experimental parameter range and is proportional to the square root of the sweep rate at the onset of labyrinthine instability.

  9. Magnetic Field Stabilization for Magnetically Shielded Volumes by External Field Coils

    PubMed Central

    Brys, T.; Czekaj, S.; Daum, M.; Fierlinger, P.; George, D.; Henneck, R.; Hochman, Z.; Kasprzak, M.; Kohlik, K.; Kirch, K.; Kuzniak, M.; Kuehne, G.; Pichlmaier, A.; Siodmok, A.; Szelc, A.; Tanner, L.

    2005-01-01

    For highly sensitive magnetic measurements, e.g., a measurement of the neutron electric dipole moment (EDM), the magnetic field has to be stable in time on a level below picoTesla. One of several measures we employ to achieve this uses an external field coil system which can stabilize the ambient external field at a predefined value. Here we report on the construction and characterization of such a system in the magnetic test facility at PSI. The system actively stabilizes the field along the axis of the EDM experiment by means of four coils in a Helmholtz-like configuration. Additional coils serve to compensate for transverse ambient field components. Because of the long integration times in the EDM experiment (about 100 s or more) only slow disturbances have to be corrected for. The performance of the system has been measured using static and moving magnetic sources and suppression factors in excess of 200 have been observed. PMID:27308117

  10. Magnetic Field Stabilization for Magnetically Shielded Volumes by External Field Coils.

    PubMed

    Brys, T; Czekaj, S; Daum, M; Fierlinger, P; George, D; Henneck, R; Hochman, Z; Kasprzak, M; Kohlik, K; Kirch, K; Kuzniak, M; Kuehne, G; Pichlmaier, A; Siodmok, A; Szelc, A; Tanner, L

    2005-01-01

    For highly sensitive magnetic measurements, e.g., a measurement of the neutron electric dipole moment (EDM), the magnetic field has to be stable in time on a level below picoTesla. One of several measures we employ to achieve this uses an external field coil system which can stabilize the ambient external field at a predefined value. Here we report on the construction and characterization of such a system in the magnetic test facility at PSI. The system actively stabilizes the field along the axis of the EDM experiment by means of four coils in a Helmholtz-like configuration. Additional coils serve to compensate for transverse ambient field components. Because of the long integration times in the EDM experiment (about 100 s or more) only slow disturbances have to be corrected for. The performance of the system has been measured using static and moving magnetic sources and suppression factors in excess of 200 have been observed. PMID:27308117

  11. Towards a beyond 1 GHz solid-state nuclear magnetic resonance: External lock operation in an external current mode for a 500 MHz nuclear magnetic resonance

    SciTech Connect

    Takahashi, Masato; Maeda, Hideaki; Ebisawa, Yusuke; Tennmei, Konosuke; Yanagisawa, Yoshinori; Nakagome, Hideki; Hosono, Masami; Takasugi, Kenji; Hase, Takashi; Miyazaki, Takayoshi; Fujito, Teruaki; Kiyoshi, Tsukasa; Yamazaki, Toshio

    2012-10-15

    Achieving a higher magnetic field is important for solid-state nuclear magnetic resonance (NMR). But a conventional low temperature superconducting (LTS) magnet cannot exceed 1 GHz (23.5 T) due to the critical magnetic field. Thus, we started a project to replace the Nb{sub 3}Sn innermost coil of an existing 920 MHz NMR (21.6 T) with a Bi-2223 high temperature superconducting (HTS) innermost coil. Unfortunately, the HTS magnet cannot be operated in persistent current mode; an external dc power supply is required to operate the NMR magnet, causing magnetic field fluctuations. These fluctuations can be stabilized by a field-frequency lock system based on an external NMR detection coil. We demonstrate here such a field-frequency lock system in a 500 MHz LTS NMR magnet operated in an external current mode. The system uses a {sup 7}Li sample in a microcoil as external NMR detection system. The required field compensation is calculated from the frequency of the FID as measured with a frequency counter. The system detects the FID signal, determining the FID frequency, and calculates the required compensation coil current to stabilize the sample magnetic field. The magnetic field was stabilized at 0.05 ppm/3 h for magnetic field fluctuations of around 10 ppm. This method is especially effective for a magnet with large magnetic field fluctuations. The magnetic field of the compensation coil is relatively inhomogeneous in these cases and the inhomogeneity of the compensation coil can be taken into account.

  12. Microwave radiation power of relativistic electron beam with virtual cathode in the external magnetic field

    NASA Astrophysics Data System (ADS)

    Kurkin, S. A.; Hramov, A. E.; Koronovskii, A. A.

    2013-07-01

    The study of the output power of the electromagnetic radiation of the relativistic electron beam (REB) with virtual cathode in the presence of external magnetic field has been found out. The typical dependencies of the output microwave power of the vircator versus external magnetic field have been analyzed by means of 3D electromagnetic simulation. It has been shown that the power of vircator demonstrates several maxima with external magnetic field growth. The characteristic features of the power behavior are determined by the conditions of the virtual cathode formation in the presence of the external transversal magnetic field and the REB self-magnetic fields.

  13. Microwave radiation power of relativistic electron beam with virtual cathode in the external magnetic field

    SciTech Connect

    Kurkin, S. A.; Hramov, A. E.; Koronovskii, A. A.; Saratov State Technical University, Politechnicheskaja 77, Saratov 410028

    2013-07-22

    The study of the output power of the electromagnetic radiation of the relativistic electron beam (REB) with virtual cathode in the presence of external magnetic field has been found out. The typical dependencies of the output microwave power of the vircator versus external magnetic field have been analyzed by means of 3D electromagnetic simulation. It has been shown that the power of vircator demonstrates several maxima with external magnetic field growth. The characteristic features of the power behavior are determined by the conditions of the virtual cathode formation in the presence of the external transversal magnetic field and the REB self-magnetic fields.

  14. Distribution of AC loss in a HTS magnet for SMES with different operating conditions

    NASA Astrophysics Data System (ADS)

    Xu, Y.; Tang, Y.; Ren, L.; Jiao, F.; Song, M.; Cao, K.; Wang, D.; Wang, L.; Dong, H.

    2013-11-01

    The AC loss induced in superconducting tape may affect the performance of a superconducting device applied to power system, such as transformer, cable, motor and even Superconducting Magnetic Energy Storage (SMES). The operating condition of SMES is changeable due to the need of compensation to the active or reactive power according to the demand of a power grid. In this paper, it is investigated that the distribution of AC loss for a storage magnet on different operating conditions, which is based on finite element method (FEM) and measured properties of BSCCO/Ag tapes. This analytical method can be used to optimize the SMES magnet.

  15. In vitro cytotoxicity of Selol-loaded magnetic nanocapsules against neoplastic cell lines under AC magnetic field activation

    NASA Astrophysics Data System (ADS)

    Falqueiro, A. M.; Siqueira-Moura, M. P.; Jardim, D. R.; Primo, F. L.; Morais, P. C.; Mosiniewicz-Szablewska, E.; Suchocki, P.; Tedesco, A. C.

    2012-04-01

    The goals of this study are to evaluate invitro compatibility of magnetic nanomaterials and their therapeutic potential against cancer cells. Highly stable ionic magnetic fluid sample (maghemite, γ-Fe2O3) and Selol were incorporated into polymeric nanocapsules by nanoprecipitation method. The cytotoxic effect of Selol-loaded magnetic nanocapsules was assessed on murine melanoma (B16-F10) and oral squamous cell carcinoma (OSCC) cell lines following AC magnetic field application. The influence of different nanocapsules on cell viability was investigated by colorimetric MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay. In the absence of AC magnetic field Selol-loaded magnetic nanocapsules, containing 100 µg/mL Selol plus 5 × 1012 particle/mL, showed antitumoral activity of about 50% on B16-F10 melanoma cells while OSCC carcinoma cells demonstrated drug resistance at all concentrations of Selol and magnetic fluid (range of 100-500 µg/mL Selol and 5 × 1012-2.5 × 1013 particle/mL). On the other hand, under AC applied fields (1 MHz and 40 Oe amplitude) B16-F10 cell viability was reduced down to 40.5% (±3.33) at the highest concentration of nanoencapsulated Selol. The major effect, however, was observed on OSCC cells since the cell viability drops down to about 33.3% (±0.38) under application of AC magnetic field. These findings clearly indicate that the Selol-loaded magnetic nanocapsules present different toxic effects on neoplastic cell lines. Further, the cytotoxic effect was maximized under AC magnetic field application on OSCC, which emphasizes the effectiveness of the magnetohyperthermia approach.

  16. Magnetic resonance imaging and computerized tomography in malignant external otitis

    SciTech Connect

    Gherini, S.G.; Brackmann, D.E.; Bradley, W.G.

    1986-05-01

    In malignant external otitis (MEO), determining the anatomic extent of disease and evaluating the physiologic response to therapy remain a problem. Magnetic resonance imaging (MRI) has recently become available in limited clinical settings. Four patients with MEO were evaluated using MRI, computerized tomography (CT), technetium-99 (Tc-99) bone scanning, and gallium-67 citrate (Ga-67 citrate) scanning. MRI is superior to CT, Tc-99 bone scanning, and Ga-67 citrate scanning in evaluating the anatomic extent of soft tissue changes in MEO. MRI alone cannot be relied upon to determine the physiologic response to therapy. MRI can, however, serve as a valuable guide to the interpretation of Tc-99 bone and Ga-67 citrate scans, and in this respect, MRI is extremely useful in the treatment of MEO.

  17. Development and application of setup for ac magnetic field in neutron scattering experiments.

    PubMed

    Klimko, Sergey; Zhernenkov, Kirill; Toperverg, Boris P; Zabel, Hartmut

    2010-10-01

    We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm(3) and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed. PMID:21034083

  18. Development and application of setup for ac magnetic field in neutron scattering experiments

    SciTech Connect

    Klimko, Sergey; Zhernenkov, Kirill; Toperverg, Boris P.; Zabel, Hartmut

    2010-10-15

    We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm{sup 3} and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed.

  19. AC driven magnetic domain quantification with 5 nm resolution.

    PubMed

    Li, Zhenghua; Li, Xiang; Dong, Dapeng; Liu, Dongping; Saito, H; Ishio, S

    2014-01-01

    As the magnetic storage density increases in commercial products, e.g. the hard disc drives, a full understanding of dynamic magnetism in nanometer resolution underpins the development of next-generation products. Magnetic force microscopy (MFM) is well suited to exploring ferromagnetic domain structures. However, atomic resolution cannot be achieved because data acquisition involves the sensing of long-range magnetostatic forces between tip and sample. Moreover, the dynamic magnetism cannot be characterized because MFM is only sensitive to the static magnetic fields. Here, we develop a side-band magnetic force microscopy (MFM) to locally observe the alternating magnetic fields in nanometer length scales at an operating distance of 1 nm. Variations in alternating magnetic fields and their relating time-variable magnetic domain reversals have been demonstrated by the side-band MFM. The magnetic domain wall motions, relating to the periodical rotation of sample magnetization, are quantified via micromagnetics. Based on the side-band MFM, the magnetic moment can be determined locally in a volume as small as 5 nanometers. The present technique can be applied to investigate the microscopic magnetic domain structures in a variety of magnetic materials, and allows a wide range of future applications, for example, in data storage and biomedicine. PMID:25011670

  20. Ultrasonic propagation velocity in magnetic and magnetorheological fluids due to an external magnetic field.

    PubMed

    Bramantya, M A; Motozawa, M; Sawada, T

    2010-08-18

    Ultrasonic propagation velocity in a magnetic fluid (MF) and magnetorheological fluid (MRF) changes with the application of an external magnetic field. The formation of clustering structures inside the MF and MRF clearly has an influence on the ultrasonic propagation velocity. Therefore, we propose a qualitative analysis of these structures by measuring properties of ultrasonic propagation. Since MF and MRF are opaque, non-contact inspection using the ultrasonic technique can be very useful for analyzing the inner structures of MF and MRF. In this study, we measured ultrasonic propagation velocity in a hydrocarbon-based MF and MRF precisely. Based on these results, the clustering structures of these fluids are analyzed experimentally in terms of elapsed time dependence and the effect of external magnetic field strength. The results reveal hysteresis and anisotropy in the ultrasonic propagation velocity. We also discuss differences of ultrasonic propagation velocity between MF and MRF. PMID:21386478

  1. Controlling surface plasmon polaritons by a static and/or time-dependent external magnetic field

    NASA Astrophysics Data System (ADS)

    Kuzmiak, V.; Eyderman, S.; Vanwolleghem, M.

    2012-07-01

    We have demonstrated numerically by using of Fourier modal method (FMM) that the interface between a metal and a uniformly magnetized two-dimensional photonic crystal fabricated from a transparent dielectric magneto-optical (MO) material possesses a one-way frequency range in which a surface plasmon polariton (SPP) is allowed to propagate only in one direction. The time-reversal symmetry breaking is implied by the MO properties of the photonic crystal material, namely, bismuth iron garnet (BIG), which may be magnetically saturated by fields of the order of tens of milli tesla. The results obtained by FMM have been validated by a theoretical model and a standard plane-wave method that yield separately a nonreciprocal dispersion relation for the SPP and the band structure of the two-dimensional magneto-optical photonic crystal (2D MOPhC), respectively. These spectra represent the key characteristics assuring the functionality of the one-way waveguide associated with the both underlying mechanisms, namely, time-reversal symmetry breaking and a suppression of disorder-induced backscattering. By using a generalized finite-difference time-domain (FDTD) method, which allows studying the propagation of electromagnetic (EM) waves through media with a tensor MO permittivity, we studied transport properties of the one-way waveguide. We examined the influence of specific types of boundary conditions on one-way functionality in the presence of a static external magnetic field and have shown that the SPP can be dynamically controlled by applying a time-dependent magnetic field. By evaluating the Fourier transform of the energy density, we have analyzed the behavior of the field patterns observed in the waveguide in the case of ac magnetic field, and have interpreted new and interesting features associated with the redistribution of the EM field that may offer new mechanisms for dynamical control of SPP flow.

  2. Encouragement of Enzyme Reaction Utilizing Heat Generation from Ferromagnetic Particles Subjected to an AC Magnetic Field

    PubMed Central

    Suzuki, Masashi; Aki, Atsushi; Mizuki, Toru; Maekawa, Toru; Usami, Ron; Morimoto, Hisao

    2015-01-01

    We propose a method of activating an enzyme utilizing heat generation from ferromagnetic particles under an ac magnetic field. We immobilize α-amylase on the surface of ferromagnetic particles and analyze its activity. We find that when α-amylase/ferromagnetic particle hybrids, that is, ferromagnetic particles, on which α-amylase molecules are immobilized, are subjected to an ac magnetic field, the particles generate heat and as a result, α-amylase on the particles is heated up and activated. We next prepare a solution, in which α-amylase/ferromagnetic particle hybrids and free, nonimmobilized chitinase are dispersed, and analyze their activities. We find that when the solution is subjected to an ac magnetic field, the activity of α-amylase immobilized on the particles increases, whereas that of free chitinase hardly changes; in other words, only α-amylase immobilized on the particles is selectively activated due to heat generation from the particles. PMID:25993268

  3. Fiber - Optic Devices as Temperature Sensors for Temperature Measurements in AC Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Rablau, Corneliu; Lafrance, Joseph; Sala, Anca

    2007-10-01

    We report on the investigation of several fiber-optic devices as potential sensors for temperature measurements in AC magnetic fields. Common temperature sensors, such as thermocouples, thermistors or diodes, will create random and/or systematic errors when placed in a magnetic field. A DC magnetic field is susceptible to create a systematic offset to the measurement, while in an AC magnetic field of variable frequency random errors which cannot be corrected for can also be introduced. Fiber-Bragg-gratings and thin film filters have an inherent temperature dependence. Detrimental for their primary applications, the same dependence allows one to use such devices as temperature sensors. In an AC magnetic field, they present the advantage of being immune to electromagnetic interference. Moreover, for fiber-Bragg-gratings, the shape factor and small mass of the bare-fiber device make it convenient for temperature measurements on small samples. We studied several thin-film filters and fiber-Bragg-gratings and compared their temperature measurement capabilities in AC magnetic fields of 0 to 150 Gauss, 0 to 20 KHz to the results provided by off-the-shelf thermocouples and thermistor-based temperature measurement systems.

  4. Nonlinear ac stationary response and dynamic magnetic hysteresis of quantum uniaxial superparamagnets

    NASA Astrophysics Data System (ADS)

    Kalmykov, Yuri P.; Titov, Serguey V.; Coffey, William T.

    2015-11-01

    The nonlinear ac stationary response of uniaxial paramagnets and superparamagnets—nanoscale solids or clusters with spin number S ˜100-104 —in superimposed uniform ac and dc bias magnetic fields of arbitrary strength, each applied along the easy axis of magnetization, is determined by solving the evolution equation for the reduced density matrix represented as a finite set of three-term differential-recurrence relations for its diagonal matrix elements. The various harmonic components arising from the nonlinear response of the magnetization, dynamic magnetic hysteresis loops, etc., are then evaluated via matrix continued fractions indicating a pronounced dependence of the response on S arising from the quantum spin dynamics, which differ markedly from the magnetization dynamics of classical nanomagnets. In the linear response approximation, the results concur with existing solutions.

  5. External magnetic field-induced selective biodistribution of magnetoliposomes in mice

    NASA Astrophysics Data System (ADS)

    García-Jimeno, Sonia; Escribano, Elvira; Queralt, Josep; Estelrich, Joan

    2012-08-01

    This study looked at the effect of an external magnet on the biodistribution of magnetoliposomes intravenously administrated in mice (8 mg iron/kg) with and without induced acute inflammation. Our results showed that due to enhanced vascular permeability, magnetoliposomes accumulated at the site of inflammation in the absence of an external magnetic field, but the amount of iron present increased under the effect of a magnet located at the inflammation zone. This increase was dependent on the time (20 or 60 min) of exposure of the external magnetic field. It was also observed that the presence of the magnet was associated with lower amounts of iron in the liver, spleen, and plasma than was found in mice in which a magnet had not been applied. The results of this study confirm that it is possible to target drugs encapsulated in magnetic particles by means of an external magnet.

  6. External magnetic field-induced selective biodistribution of magnetoliposomes in mice

    PubMed Central

    2012-01-01

    This study looked at the effect of an external magnet on the biodistribution of magnetoliposomes intravenously administrated in mice (8 mg iron/kg) with and without induced acute inflammation. Our results showed that due to enhanced vascular permeability, magnetoliposomes accumulated at the site of inflammation in the absence of an external magnetic field, but the amount of iron present increased under the effect of a magnet located at the inflammation zone. This increase was dependent on the time (20 or 60 min) of exposure of the external magnetic field. It was also observed that the presence of the magnet was associated with lower amounts of iron in the liver, spleen, and plasma than was found in mice in which a magnet had not been applied. The results of this study confirm that it is possible to target drugs encapsulated in magnetic particles by means of an external magnet. PMID:22883385

  7. The suppression effect of external magnetic field on the high-power microwave window multipactor phenomenon

    SciTech Connect

    Zhang, Xue Wang, Yong; Fan, Junjie

    2015-02-15

    To suppress the surface multipactor phenomenon and improve the transmitting power of the high-power microwave window, the application of external magnetic fields is theoretically analyzed and simulated. A Monte Carlo algorithm is used to track the secondary electron trajectories and study the multipactor scenario on the surface of a cylinder window. It is confirmed that over-resonant magnetic fields (an external magnetic field whose magnitude is slightly greater than that of a resonant magnetic field) will generate a compensating trajectory and collision, which can suppress the secondary electron avalanche. The optimal value of this external magnetic field that will avoid the multipactor phenomenon on cylinder windows is discussed.

  8. Magnetized particle motion around non-Schwarzschild black hole immersed in an external uniform magnetic field

    NASA Astrophysics Data System (ADS)

    Rayimbaev, J. R.

    2016-09-01

    The motion of a magnetized particle orbiting around non-Schwarzschild black hole immersed in an external uniform magnetic field is considered. The influence of deformation parameter h to effective potential of the radial motion of the magnetized particle around non-Schwarzschild black hole using Hamilton-Jacobi formalism is studied. We have obtained numerical values of area Δ ρ where magnetized particles can move which is expanding (narrowing) due to the effect of the negative (positive) deformation. Finally, we have studied the collision of two particles (magnetized-neutral, magnetized-magnetized, magnetized-charged) in non-Schwarzschild spacetime and got the center-of-mass energy (E_{c.m}) for the particles. Moreover, we have found the capture radius (r_{cap}) - the distance from the central object to the point where particles collide and fall down to the central compact object. It is shown that non-Schwarzschild black holes could also act as particle accelerators with arbitrarily high center-of-mass energy.

  9. Study on a magnetic spiral-type wireless capsule endoscope controlled by rotational external permanent magnet

    NASA Astrophysics Data System (ADS)

    Ye, Bo; Zhang, Wei; Sun, Zhen-jun; Guo, Lin; Deng, Chao; Chen, Ya-qi; Zhang, Hong-hai; Liu, Sheng

    2015-12-01

    In this paper, the authors propose rotating an external permanent magnet (EPM) to manipulate the synchronous rotation of a magnetic spiral-type wireless capsule endoscope (WCE), and the synchronous rotation of the WCE is converted to its translational motion in intestinal tract. In order to preliminarily verify the feasibility of this method, a handheld actuator (HA) controlled by micro controller unit, a magnetic spiral-type WCE and a bracket were fabricated, theoretical analysis and simulations about the control distance of this method were performed, and in ex-vivo tests were examined in porcine small intestine to verify the control distance and control performances of this method. It was demonstrated that this method showed good performances in controlling the translational motion of the magnetic spiral-type WCE, and this method has great potential to be used in clinical application.

  10. Magnetic Reconnection of an Externally Applied Magnetic Field in a High-Energy Density Plasma

    NASA Astrophysics Data System (ADS)

    Fiksel, G.; Barnak, D.; Chang, P.-Y.; Hu, S. X.; Nilson, P. M.; Betti, R.; Fox, W.; Germaschewski, K.; Bhattacharjee, A.

    2013-10-01

    An experiment on magnetic reconnection of an externally applied magnetic field in counter-propagating high-energy density plasmas was conducted on the OMEGA EP Laser System. Two counter-propagating plasma flows were created by irradiating oppositely placed plastic (CH) targets with 1.8-kJ, 2-ns laser beams. An external magnetic field was imposed perpendicular to the plasma flow by MIFEDS (magneto-inertial fusion electrical discharge system). The magnetic field has a null-x-point geometry with B = 5 T at the targets. The plasma interaction was imaged by laser-driven, fast-proton radiography. The radiography images demonstrate formation of a pair of counter-propagating magnetized ``ribbons'' that collide and reconnect at the midplane. The results will be compared with particle-in-cell simulations and interpreted with predictions from the DRACO code. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944, and NLUF Grant DE-SC0008655.

  11. Propagation of magnetic avalanches in Mn12Ac at high field sweep rates.

    PubMed

    Decelle, W; Vanacken, J; Moshchalkov, V V; Tejada, J; Hernández, J M; Macià, F

    2009-01-16

    Time-resolved measurements of the magnetization reversal in single crystals of Mn12Ac in pulsed magnetic fields, at magnetic field sweep rates from 1.5 kT/s up to 7 kT/s, suggest a new process that cannot be scaled onto a deflagrationlike propagation driven by heat diffusion. The sweep rate dependence of the propagation velocity, increasing from a few 100 m/s up to the speed of sound in Mn12Ac, indicates the existence of two new regimes at the highest sweep rates, with a transition around 4 kT/s that can be understood as a magnetic deflagration-to-detonation transition. PMID:19257315

  12. External Electromagnetic Fields of a Slowly Rotating Magnetized Star with Nonvanishing Gravitomagnetic Charge

    NASA Astrophysics Data System (ADS)

    Ahmedov, B. J.; Khugaev, A. V.; Rakhmatov, N. I.

    2008-09-01

    We write Maxwell equations in the external background spacetime of a slowly rotating magnetized NUT star and find analytical solutions after separating them into angular and radial parts. The star is considered isolated and in vacuum, with monopolar configuration model for the stellar magnetic field. The contribution to the external field from the NUT charge and frame-dragging effect are considered in detail.

  13. Self-consistent magnetic properties of magnetite tracers optimized for magnetic particle imaging measured by ac susceptometry, magnetorelaxometry and magnetic particle spectroscopy

    PubMed Central

    Ludwig, Frank; Remmer, Hilke; Kuhlmann, Christian; Wawrzik, Thilo; Arami, Hamed; Ferguson, R. Mathew; Krishnan, Kannan M.

    2015-01-01

    Sensitivity and spatial resolution in Magnetic Particle Imaging are affected by magnetic properties of the nanoparticle tracers used during imaging. Here, we have carried out a comprehensive magnetic characterization of single-core iron oxide nanoparticles that were designed for MPI. We used ac susceptometry, fluxgate magnetorelaxometry, and magnetic particle spectroscopy to evaluate the tracer’s magnetic core size, hydrodynamic size, and magnetic anisotropy. Our results present a self-consistent set of magnetic and structural parameters for the tracers that is consistent with direct measurements of size using transmission electron microscopy and dynamic light scattering and that can be used to better understand their MPI performance. PMID:25729125

  14. Self-consistent magnetic properties of magnetite tracers optimized for magnetic particle imaging measured by ac susceptometry, magnetorelaxometry and magnetic particle spectroscopy

    NASA Astrophysics Data System (ADS)

    Ludwig, Frank; Remmer, Hilke; Kuhlmann, Christian; Wawrzik, Thilo; Arami, Hamed; Ferguson, R. Mathew; Krishnan, Kannan M.

    2014-06-01

    Sensitivity and spatial resolution in magnetic particle imaging are affected by magnetic properties of the nanoparticle tracers used during imaging. Here, we have carried out a comprehensive magnetic characterization of single-core iron oxide nanoparticles that were designed for MPI. We used ac susceptometry, fluxgate magnetorelaxometry, and magnetic particle spectroscopy to evaluate the tracer's magnetic core size, hydrodynamic size, and magnetic anisotropy. Our results present a self-consistent set of magnetic and structural parameters for the tracers that is consistent with direct measurements of size using transmission electron microscopy and dynamic light scattering and that can be used to better understand their MPI performance.

  15. Quantitatively probing the magnetic behavior of individual nanoparticles by an AC field-modulated magnetic force microscopy.

    PubMed

    Li, Xiang; Lu, Wei; Song, Yiming; Wang, Yuxin; Chen, Aiying; Yan, Biao; Yoshimura, Satoru; Saito, Hitoshi

    2016-01-01

    Despite decades of advances in magnetic imaging, obtaining direct, quantitative information with nanometer scale spatial resolution remains an outstanding challenge. Current approaches, for example, Hall micromagnetometer and nitrogen-vacancy magnetometer, are limited by highly complex experimental apparatus and a dedicated sample preparation process. Here we present a new AC field-modulated magnetic force microscopy (MFM) and report the local and quantitative measurements of the magnetic information of individual magnetic nanoparticles (MNPs), which is one of the most iconic objects of nanomagnetism. This technique provides simultaneously a direct visualization of the magnetization process of the individual MNPs, with spatial resolution and magnetic sensitivity of about 4.8 nm and 1.85 × 10(-20) A m(2), respectively, enabling us to separately estimate the distributions of the dipolar fields and the local switching fields of individual MNPs. Moreover, we demonstrate that quantitative magnetization moment of individual MNPs can be routinely obtained using MFM signals. Therefore, it underscores the power of the AC field-modulated MFM for biological and biomedical applications of MNPs and opens up the possibility for directly and quantitatively probing the weak magnetic stray fields from nanoscale magnetic systems with superior spatial resolution. PMID:26932357

  16. Quantitatively probing the magnetic behavior of individual nanoparticles by an AC field-modulated magnetic force microscopy

    PubMed Central

    Li, Xiang; Lu, Wei; Song, Yiming; Wang, Yuxin; Chen, Aiying; Yan, Biao; Yoshimura, Satoru; Saito, Hitoshi

    2016-01-01

    Despite decades of advances in magnetic imaging, obtaining direct, quantitative information with nanometer scale spatial resolution remains an outstanding challenge. Current approaches, for example, Hall micromagnetometer and nitrogen-vacancy magnetometer, are limited by highly complex experimental apparatus and a dedicated sample preparation process. Here we present a new AC field-modulated magnetic force microscopy (MFM) and report the local and quantitative measurements of the magnetic information of individual magnetic nanoparticles (MNPs), which is one of the most iconic objects of nanomagnetism. This technique provides simultaneously a direct visualization of the magnetization process of the individual MNPs, with spatial resolution and magnetic sensitivity of about 4.8 nm and 1.85 × 10−20 A m2, respectively, enabling us to separately estimate the distributions of the dipolar fields and the local switching fields of individual MNPs. Moreover, we demonstrate that quantitative magnetization moment of individual MNPs can be routinely obtained using MFM signals. Therefore, it underscores the power of the AC field-modulated MFM for biological and biomedical applications of MNPs and opens up the possibility for directly and quantitatively probing the weak magnetic stray fields from nanoscale magnetic systems with superior spatial resolution. PMID:26932357

  17. Quantitatively probing the magnetic behavior of individual nanoparticles by an AC field-modulated magnetic force microscopy

    NASA Astrophysics Data System (ADS)

    Li, Xiang; Lu, Wei; Song, Yiming; Wang, Yuxin; Chen, Aiying; Yan, Biao; Yoshimura, Satoru; Saito, Hitoshi

    2016-03-01

    Despite decades of advances in magnetic imaging, obtaining direct, quantitative information with nanometer scale spatial resolution remains an outstanding challenge. Current approaches, for example, Hall micromagnetometer and nitrogen-vacancy magnetometer, are limited by highly complex experimental apparatus and a dedicated sample preparation process. Here we present a new AC field-modulated magnetic force microscopy (MFM) and report the local and quantitative measurements of the magnetic information of individual magnetic nanoparticles (MNPs), which is one of the most iconic objects of nanomagnetism. This technique provides simultaneously a direct visualization of the magnetization process of the individual MNPs, with spatial resolution and magnetic sensitivity of about 4.8 nm and 1.85 × 10-20 A m2, respectively, enabling us to separately estimate the distributions of the dipolar fields and the local switching fields of individual MNPs. Moreover, we demonstrate that quantitative magnetization moment of individual MNPs can be routinely obtained using MFM signals. Therefore, it underscores the power of the AC field-modulated MFM for biological and biomedical applications of MNPs and opens up the possibility for directly and quantitatively probing the weak magnetic stray fields from nanoscale magnetic systems with superior spatial resolution.

  18. Externalities.

    ERIC Educational Resources Information Center

    Zicht, Barbara, Ed.; And Others

    1982-01-01

    This issue explains the concept of externalities (benefits or burdens which accrue to society when there is a difference between the private cost or benefit of an action and the social cost or benefit of that action). These external or social costs of individual actions are often referred to as spillover costs. Three brief teaching units follow…

  19. Mitigating stimulated scattering processes in gas-filled Hohlraums via external magnetic fields

    SciTech Connect

    Gong, Tao; Zheng, Jian; Li, Zhichao; Ding, Yongkun; Yang, Dong; Hu, Guangyue; Zhao, Bin

    2015-09-15

    A simple model, based on energy and pressure equilibrium, is proposed to deal with the effect of external magnetic fields on the plasma parameters inside the laser path, which shows that the electron temperature can be significantly enhanced as the intensity of the external magnetic fields increases. With the combination of this model and a 1D three-wave coupling code, the effect of external magnetic fields on the reflectivities of stimulated scattering processes is studied. The results indicate that a magnetic field with an intensity of tens of Tesla can decrease the reflectivities of stimulated scattering processes by several orders of magnitude.

  20. External magnetic fields affect the biological impacts of superparamagnetic iron nanoparticles.

    PubMed

    Shanehsazzadeh, Saeed; Lahooti, Afsaneh; Hajipour, Mohammad Javad; Ghavami, Mahdi; Azhdarzadeh, Morteza

    2015-12-01

    Superparamagnetic iron oxide nanoparticles (SPIONs) are recognized as one of the promising nanomaterials for applications in various field of nanomedicine such as targeted imaging/drug delivery, tissue engineering, hyperthermia, and gene therapy. Besides their suitable biocompatibility, SPIONs' unique magnetic properties make them an outstanding candidate for theranostic nanomedicine. Very recent progress in the field revealed that the presence of external magnetic fields may cause considerable amount of SPIONs' agglomeration in their colloidal suspension. As variation of physicochemical properties of colloidal nanoparticles has strong effect on their biological outcomes, one can expect that the SPIONs' agglomeration in the presence of external magnetic fields could change their well-recognized biological impacts. In this case, here, we probed the cellular uptake and toxicity of the SPIONs before and after exposure to external magnetic fields. We found that the external magnetic fields can affect the biological outcome of magnetic nanoparticles. PMID:26613856

  1. Numerical study on AC loss characteristics of superconducting power transmission cables comprising coated conductors with magnetic substrates

    NASA Astrophysics Data System (ADS)

    Amemiya, N.; Nakahata, M.

    2007-10-01

    Electromagnetic field analyses were made for mono-layer conductors comprising coated conductors for superconducting power transmission cables in order to evaluate their AC loss characteristics. We focused on the magnetic properties of the substrates of coated conductors. The current distribution in each coated conductor and the magnetic flux profile around each coated conductor were visualized. The influence of relative permeability and the space between coated conductors on the AC loss characteristics of mono-layer conductors were studied based on the visualized current and magnetic flux distributions. The influence of a saturated magnetic property on a calculated AC loss was also discussed.

  2. Influence of external magnetic field on dynamics of open quantum systems

    SciTech Connect

    Kalandarov, Sh. A.; Kanokov, Z.; Adamian, G. G.; Antonenko, N. V.

    2007-03-15

    The influence of an external magnetic field on the non-Markovian dynamics of an open two-dimensional quantum system is investigated. The fluctuations of collective coordinate and momentum and transport coefficients are studied for a charged harmonic oscillator linearly coupled to a neutral bosonic heat bath. It is shown that the dissipation of collective energy slows down with increasing strength of the external magnetic field. The role of magnetic field in the diffusion processes is illustrated by several examples.

  3. Stable solitary waves in super dense plasmas at external magnetic fields

    NASA Astrophysics Data System (ADS)

    Ghaani, Azam; Javidan, Kurosh; Sarbishaei, Mohsen

    2015-07-01

    Propagation of localized waves in a Fermi-Dirac distributed super dense matter at the presence of strong external magnetic fields is studied using the reductive perturbation method. We have shown that stable solitons can be created in such non-relativistic fluids in the presence of an external magnetic field. Such solitary waves are governed by the Zakharov-Kuznetsov (ZK) equation. Properties of solitonic solutions are studied in media with different values of background mass density and strength of magnetic field.

  4. Spin-lattice dynamics simulation of external field effect on magnetic order of ferromagnetic iron

    SciTech Connect

    Chui, C. P.; Zhou, Yan

    2014-03-15

    Modeling of field-induced magnetization in ferromagnetic materials has been an active topic in the last dozen years, yet a dynamic treatment of distance-dependent exchange integral has been lacking. In view of that, we employ spin-lattice dynamics (SLD) simulations to study the external field effect on magnetic order of ferromagnetic iron. Our results show that an external field can increase the inflection point of the temperature. Also the model provides a better description of the effect of spin correlation in response to an external field than the mean-field theory. An external field has a more prominent effect on the long range magnetic order than on the short range counterpart. Furthermore, an external field allows the magnon dispersion curves and the uniform precession modes to exhibit magnetic order variation from their temperature dependence.

  5. Targeting of systemically-delivered magnetic nanoparticle hyperthermia using a noninvasive, static, external magnetic field

    NASA Astrophysics Data System (ADS)

    Zulauf, Grayson D.; Trembly, B. Stuart; Giustini, Andrew J.; Flint, Brian R.; Strawbridge, Rendall R.; Hoopes, P. Jack

    2013-02-01

    One of the greatest challenges of nanoparticle cancer therapy is the delivery of adequate numbers of nanoparticles to the tumor site. Iron oxide nanoparticles (IONPs) have many favorable qualities, including their nontoxic composition, the wide range of diameters in which they can be produced, the cell-specific cytotoxic heating that results from their absorption of energy from a nontoxic, external alternating magnetic field (AMF), and the wide variety of functional coatings that can be applied. Although IONPs can be delivered via an intra-tumoral injection to some tumors, the resulting tumor IONP distribution is generally inadequate; additionally, local tumor injections do not allow for the treatment of systemic or multifocal disease. Consequently, the ultimate success of nanoparticle based cancer therapy likely rests with successful systemic, tumor-targeted IONP delivery. In this study, we used a surface-based, bilateral, noninvasive static magnetic field gradient produced by neodymiumboron- iron magnets (80 T/m to 130 T/m in central plane between magnets), a rabbit ear model, and systemicallydelivered starch-coated 100 nm magnetic (iron oxide) nanoparticles to demonstrate a spatially-defined increase in the local tissue accumulation of IONPs. In this non-tumor model, the IONPs remained within the local vascular space. It is anticipated that this technique can be used to enhance IONP delivery significantly to the tumor parenchyma/cells.

  6. A self-powered AC magnetic sensor based on piezoelectric nanogenerator

    NASA Astrophysics Data System (ADS)

    Yu, Aifang; Song, Ming; Zhang, Yan; Kou, Jinzong; Zhai, Junyi; Wang, Zhong Lin

    2014-11-01

    An AC magnetic field, which is a carrier of information, is distributed everywhere and is continuous. How to use and detect this field has been an ongoing topic over the past few decades. Conventional magnetic sensors are usually based on the Hall Effect, the fluxgate, a superconductor quantum interface or magnetoelectric or magnetoresistive sensing. Here, a flexible, simple, low-cost and self-powered active piezoelectric nanogenerator (NG) is successfully demonstrated as an AC magnetic field sensor at room temperature. The amplitude and frequency of a magnetic field can both be accurately sensed by the NG. The output voltage of the NG has a good linearity with a measured magnetic field. The detected minute magnetic field is as low as 1.2 × 10-7 tesla, which is 400 times greater than a commercial magnetic sensor that uses the Hall Effect. In comparison to the existing technologies, an NG is a room-temperature self-powered active sensor that is very simple and very cheap for practical applications.

  7. A self-powered AC magnetic sensor based on piezoelectric nanogenerator.

    PubMed

    Yu, Aifang; Song, Ming; Zhang, Yan; Kou, Jinzong; Zhai, Junyi; Lin Wang, Zhong

    2014-11-14

    An AC magnetic field, which is a carrier of information, is distributed everywhere and is continuous. How to use and detect this field has been an ongoing topic over the past few decades. Conventional magnetic sensors are usually based on the Hall Effect, the fluxgate, a superconductor quantum interface or magnetoelectric or magnetoresistive sensing. Here, a flexible, simple, low-cost and self-powered active piezoelectric nanogenerator (NG) is successfully demonstrated as an AC magnetic field sensor at room temperature. The amplitude and frequency of a magnetic field can both be accurately sensed by the NG. The output voltage of the NG has a good linearity with a measured magnetic field. The detected minute magnetic field is as low as 1.2 × 10(-7) tesla, which is 400 times greater than a commercial magnetic sensor that uses the Hall Effect. In comparison to the existing technologies, an NG is a room-temperature self-powered active sensor that is very simple and very cheap for practical applications. PMID:25333328

  8. Properties of the resonant tunneling diode in external magnetic field with inclusion of the Rashba effect

    NASA Astrophysics Data System (ADS)

    Niketić, Nemanja; Milanović, Vitomir; Radovanović, Jelena

    2014-07-01

    Influence of the Rashba effect on electronic properties of resonant tunneling diode in an external magnetic field is analyzed in this paper. Wave functions and energies, as well as expressions for currents densities, are determined for electrons of both spins. Appearances of many modes due to the external magnetic field induce irregularities in the current-voltage characteristics, which are observable in case when the thermal energy is lower than, or comparable to, the energy difference of two consecutive Landau levels. Current density through the heterostructure is investigated with emphasis on the degree of spin polarization; further, spin transfer is shown to depend on the direction of external magnetic field.

  9. New Technique of AC drive in Tokamak using Permanent Magnets

    NASA Astrophysics Data System (ADS)

    Matteucci, Jackson; Zolfaghari, Ali

    2013-10-01

    This study investigates a new technique of capturing the rotational energy of alternating permanent magnets in order to inductively drive an alternating current in tokamak devices. The use of rotational motion bypasses many of the pitfalls seen in typical inductive and non-inductive current drives. Three specific designs are presented and assessed in the following criteria: the profile of the current generated, the RMS loop voltage generated as compared to the RMS power required to maintain it, the system's feasibility from an engineering perspective. All of the analysis has been done under ideal E&M conditions using the Maxwell 3D program. Preliminary results indicate that it is possible to produce an over 99% purely toroidal current with a RMS d Φ/dt of over 150 Tm2/s, driven by 20 MW or less of rotational power. The proposed mechanism demonstrates several key advantages including an efficient mechanical drive system, the generation of pure toroidal currents, and the potential for a quasi-steady state fusion reactor. The following quantities are presented for various driving frequencies and magnet strengths: plasma current generated, loop voltage, torque and power required. This project has been supported by DOE Funding under the SULI program.

  10. Tuning of random lasers by means of external magnetic fields based on the Voigt effect

    NASA Astrophysics Data System (ADS)

    Ghasempour Ardakani, Abbas; Mahdavi, Seyed Mohammad; Bahrampour, Ali Reza

    2013-04-01

    It has been proposed that emission spectrum of random lasers with magnetically active semiconductor constituents can be made tunable by external magnetic fields. By employing the FDTD method, the spectral intensity and spatial distribution of electric field are calculated in the presence of an external magnetic field. It is numerically shown that due to the magneto-optical Voigt effect, the emission spectrum of a semiconductor-based random laser can be made tunable by adjusting the external magnetic field. The effect of magnetic field on the localization length of the laser modes is investigated. It is also shown that the spatial distribution of electric field exhibited remarkable modification with variation of magnetic field.

  11. Late gadolinium enhanced cardiovascular magnetic resonance of lamin A/C gene mutation related dilated cardiomyopathy

    PubMed Central

    2011-01-01

    Background The purpose of this study was to identify early features of lamin A/C gene mutation related dilated cardiomyopathy (DCM) with cardiovascular magnetic resonance (CMR). We characterise myocardial and functional findings in carriers of lamin A/C mutation to facilitate the recognition of these patients using this method. We also investigated the connection between myocardial fibrosis and conduction abnormalities. Methods Seventeen lamin A/C mutation carriers underwent CMR. Late gadolinium enhancement (LGE) and cine images were performed to evaluate myocardial fibrosis, regional wall motion, longitudinal myocardial function, global function and volumetry of both ventricles. The location, pattern and extent of enhancement in the left ventricle (LV) myocardium were visually estimated. Results Patients had LV myocardial fibrosis in 88% of cases. Segmental wall motion abnormalities correlated strongly with the degree of enhancement. Myocardial enhancement was associated with conduction abnormalities. Sixty-nine percent of our asymptomatic or mildly symptomatic patients showed mild ventricular dilatation, systolic failure or both in global ventricular analysis. Decreased longitudinal systolic LV function was observed in 53% of patients. Conclusions Cardiac conduction abnormalities, mildly dilated LV and depressed systolic dysfunction are common in DCM caused by a lamin A/C gene mutation. However, other cardiac diseases may produce similar symptoms. CMR is an accurate tool to determine the typical cardiac involvement in lamin A/C cardiomyopathy and may help to initiate early treatment in this malignant familiar form of DCM. PMID:21689390

  12. Collective modes, ac response, and magnetic properties of the three-dimensional Dirac semimetal in the triplet superconducting state

    NASA Astrophysics Data System (ADS)

    Rosenstein, B.; Shapiro, B. Ya.; Shapiro, I.

    2015-08-01

    It was recently shown that conventional phonon-electron interactions may induce a triplet pairing state in time-reversal invariant three-dimensional Dirac semimetals. Starting from the microscopic model of the isotropic Dirac semimetal, the Ginzburg-Landau equations for the vector order parameter is derived using the Gor'kov technique. The collective modes including gapless Goldstone modes and gapped Higgs modes of various polarizations are identified. They are somewhat analogous to the modes in the B phase of He3, although in the present case quantitatively there is a pronounced difference between longitudinal and transverse components. The difference is caused by the vector nature of the order parameter leading to two different coherence lengths or penetration depths. The system is predicted to be highly dissipative due to the Goldstone modes. The time-dependent Ginzburg-Landau model in the presence of external fields is used to investigate some optical and magnetic properties of such superconductors. The ac conductivity of a clean sample depends on the orientation of the order parameter. It is demonstrated that the difference between the penetration depths results in rotation of the polarization vector of microwave passing a slab made of this material. The upper critical magnetic field Hc 2 was found. It turns out that at fields close to Hc 2 the order parameter orients itself perpendicular to the field direction. In certain range of parameters the triplet superconducting phase persists at arbitrarily high magnetic field like in some p -wave superconductors.

  13. Preparation of highly anisotropic cobalt ferrite/silica microellipsoids using an external magnetic field.

    PubMed

    Abramson, Sébastien; Dupuis, Vincent; Neveu, Sophie; Beaunier, Patricia; Montero, David

    2014-08-01

    Magnetic cobalt ferrite/silica microparticles having both an original morphology and an anisotropic nanostructure are synthesized through the use of an external magnetic field and nanoparticles characterized by a high magnetic anisotropy. The association of these two factors implies that the ESE (emulsion and solvent evaporation) sol-gel method employed here allows the preparation of silica microellipsoids containing magnetic nanoparticles aggregated in large chains. It is clearly shown that without this combination, microspheres characterized by an isotropic distribution of the magnetic nanoparticles are obtained. While the chaining of the cobalt ferrite nanoparticles inside the silica matrix is related to the increase of their magnetic dipolar interactions, the ellipsoidal shape of the microparticles may be explained by the elongation of the sol droplets in the direction of the external magnetic field during the synthesis. Because of their highly anisotropic structure, these microparticles exhibit permanent magnetic moments, which are responsible, at a larger scale, for the existence of strong magnetic dipolar interactions. Therefore, when they are dispersed in water, the microellipsoids self-assemble into large and irregular chains. These interactions can be reinforced by the use of external magnetic field, allowing the preparation of very large permanent chains. This research illustrates how nanostructured particles exhibiting complex architectures can be elaborated through simple, fast, and low-cost methods, such as the use of external fields in combination with soft chemistry. PMID:25029515

  14. A General Method for Calculating the External Magnetic Field from a Cylindrical Magnetic Source using Toroidal Functions

    SciTech Connect

    J Selvaggi; S Salon; O Kwon CVK Chari

    2006-02-14

    An alternative method is developed to compute the magnetic field from a circular cylindrical magnetic source. Specifically, a Fourier series expansion whose coefficients are toroidal functions is introduced which yields an alternative to the more familiar spherical harmonic solution or the Elliptic integral solution. This alternate formulation coupled with a method called charge simulation allows one to compute the external magnetic field from an arbitrary magnetic source in terms of a toroidal expansion. This expansion is valid on any finite hypothetical external observation cylinder. In other words, the magnetic scalar potential or the magnetic field intensity is computed on a exterior cylinder which encloses the magnetic source. This method can be used to accurately compute the far field where a finite element formulation is known to be inaccurate.

  15. Advanced AC permanent magnet axial flux disc motor for electric passenger vehicle

    NASA Technical Reports Server (NTRS)

    Kliman, G. B.

    1982-01-01

    An ac permanent magnet axial flux disc motor was developed to operate with a thyristor load commutated inverter as part of an electric vehicle drive system. The motor was required to deliver 29.8 kW (40 hp) peak and 10.4 kW (14 hp) average with a maximum speed of 11,000 rpm. It was also required to run at leading power factor to commutate the inverter. Three motors were built.

  16. External electromagnetic fields of a slowly rotating magnetized star with gravitomagnetic charge

    NASA Astrophysics Data System (ADS)

    Ahmedov, B. J.; Khugaev, A. V.; Abdujabbarov, A. A.

    2012-02-01

    We study Maxwell equations in the external background spacetime of a slowly rotating magnetized NUT star and find analytical solutions for the exterior electric fields after separating the equations for electric field into angular and radial parts in the lowest order in angular momentum and NUT charge approximation. The star is considered isolated and in vacuum, with dipolar magnetic field aligned with the axis of rotation. The contribution to the external electric field of star from the NUT charge is considered in detail.

  17. Thermal entanglement in a four-qubit Heisenberg spin model with external magnetic fields

    NASA Astrophysics Data System (ADS)

    Wu, Ke-Dong; Zhou, Bin; Cao, Wan-Qiang

    2007-03-01

    The entanglement properties both in the four-qubit anisotropic Heisenberg XY chain with uniform external magnetic fields and in the Heisenberg XX model with two external fields are investigated. The analytical expressions for the measures of entanglement are obtained. In Heisenberg XY chain, the effects of the anisotropy on the thermal entanglement are studied. In the Heisenberg XX ring with two external fields, it is found that a high pair entanglement can be obtained.

  18. Gastrointestinal transit and disintegration of enteric coated magnetic tablets assessed by ac biosusceptometry.

    PubMed

    Corá, Luciana A; Romeiro, Fernando G; Américo, Madileine F; Oliveira, Ricardo Brandt; Baffa, Oswaldo; Stelzer, Murilo; Miranda, José Ricardo de Arruda

    2006-01-01

    The oral administration is a common route in the drug therapy and the solid pharmaceutical forms are widely used. Although much about the performance of these formulations can be learned from in vitro studies using conventional methods, evaluation in vivo is essential in product development. The knowledge of the gastrointestinal transit and how the physiological variables can interfere with the disintegration and drug absorption is a prerequisite for development of dosage forms. The aim of this work was to employing the ac biosusceptometry (ACB) to monitoring magnetic tablets in the human gastrointestinal tract and to obtain the magnetic images of the disintegration process in the colonic region. The ac biosusceptometry showed accuracy in the quantification of the gastric residence time, the intestinal transit time and the disintegration time (DT) of the magnetic formulations in the human gastrointestinal tract. Moreover, ac biosusceptometry is a non-invasive technique, radiation-free and harmless to the volunteers, as well as an important research tool in the pharmaceutical, pharmacological and physiological investigations. PMID:16188432

  19. Brass plasmoid in external magnetic field at different air pressures

    SciTech Connect

    Patel, D. N.; Thareja, Raj K.; Pandey, Pramod K.

    2013-10-15

    The behavior of expanding brass plasmoid generated by 266 nm wavelength of Nd:YAG laser in nonuniform magnetic field at different air pressures has been examined using optical emission spectroscopy and fast imaging of plasma plumes. The splitting of the plasma plumes and enhancement of intensity of Cu I at 510.5 nm in the presence of magnetic field at lower pressures are discussed. The threading and expulsion of the magnetic field lines through the plasmoid are correlated with the ambient pressure. The stoichiometry of the plasma plume is not significantly influenced by the magnetic field; however, the abundance of neutral to ionic species of Cu and Zn is greatly influenced by the magnetic field.

  20. A wide-frequency range AC magnetometer to measure the specific absorption rate in nanoparticles for magnetic hyperthermia

    NASA Astrophysics Data System (ADS)

    Garaio, E.; Collantes, J. M.; Garcia, J. A.; Plazaola, F.; Mornet, S.; Couillaud, F.; Sandre, O.

    2014-11-01

    Measurement of specific absorption rate (SAR) of magnetic nanoparticles is crucial to assert their potential for magnetic hyperthermia. To perform this task, calorimetric methods are widely used. However, those methods are not very accurate and are difficult to standardize. In this paper, we present AC magnetometry results performed with a lab-made magnetometer that is able to obtain dynamic hysteresis-loops in the AC magnetic field frequency range from 50 kHz to 1 MHz and intensities up to 24 kA m-1. In this work, SAR values of maghemite nanoparticles dispersed in water are measured by AC magnetometry. The so-obtained values are compared with the SAR measured by calorimetric methods. Both measurements, by calorimetry and magnetometry, are in good agreement. Therefore, the presented AC magnetometer is a suitable way to obtain SAR values of magnetic nanoparticles.

  1. Calculating transport AC losses in stacks of high temperature superconductor coated conductors with magnetic substrates using FEM

    NASA Astrophysics Data System (ADS)

    Ainslie, Mark D.; Flack, Tim J.; Campbell, Archie M.

    2012-01-01

    In this paper, the authors investigate the electromagnetic properties of stacks of high temperature superconductor (HTS) coated conductors with a particular focus on calculating the total transport AC loss. The cross-section of superconducting cables and coils is often modeled as a two-dimensional stack of coated conductors, and these stacks can be used to estimate the AC loss of a practical device. This paper uses a symmetric two dimensional (2D) finite element model based on the H formulation, and a detailed investigation into the effects of a magnetic substrate on the transport AC loss of a stack is presented. The number of coated conductors in each stack is varied from 1 to 150, and three types of substrate are compared: non-magnetic weakly magnetic and strongly magnetic. The non-magnetic substrate model is comparable with results from existing models for the limiting cases of a single tape (Norris) and an infinite stack (Clem). The presence of a magnetic substrate increases the total AC loss of the stack, due to an increased localized magnetic flux density, and the stronger the magnetic material, the further the flux penetrates into the stack overall. The AC loss is calculated for certain tapes within the stack, and the differences and similarities between the losses throughout the stack are explained using the magnetic flux penetration and current density distributions in those tapes. The ferromagnetic loss of the substrate itself is found to be negligible in most cases, except for small magnitudes of current. Applying these findings to practical applications, where AC transport current is involved, superconducting coils should be wound where possible using coated conductors with a non-magnetic substrate to reduce the total AC loss in the coil.

  2. Small-size controlled vacuum spark-gap in an external magnetic field

    SciTech Connect

    Asyunin, V. I. Davydov, S. G.; Dolgov, A. N. Pshenichnyi, A. A.; Yakubov, R. Kh.

    2015-02-15

    It is demonstrated that the operation of a small-size controlled spark-gap can be controlled by applying a uniform external magnetic field. It is shown that the magnetic field of such a simple configuration efficiently suppresses the effect of localization of the discharge current after multiple actuations of the spark-gap.

  3. Influence of Weak External Magnetic Field on Amorphous and Nanocrystalline Fe-based Alloys

    SciTech Connect

    Degmova, J.; Sitek, J.

    2010-07-13

    Nanoperm, Hitperm and Finamet amorphous and nanocrystalline alloys were measured by Moessbauer spectrometry in a weak external magnetic field of 0.5 T. It was shown that the most sensitive parameters of Moessbauer spectra are the intensities of the 2nd and the 5th lines. Rather small changes were observed also in the case of internal magnetic field values. The spectrum of nanocrystalline Nanoperm showed the increase in A{sub 23} parameter (ratio of line intensities) from 2.4 to 3.7 and decrease of internal magnetic field from 20 to 19 T for amorphous subspectrum under the influence of magnetic field. Spectrum of nanocrystalline Finemet shown decrease in A{sub 23} parameter from 3.5 to 2.6 almost without a change in the internal magnetic field value. In the case of amorphous Nanoperm and Finemet samples, the changes are almost negligible. Hitperm alloy showed the highest sensitivity to the weak magnetic field, when the A{sub 23} parameter increased from 0.4 to 2.5 in the external magnetic fields. The A{sub 23} parameter of crystalline subspectrum increased from 2.7 to 3.8 and the value of internal magnetic field corresponding to amorphous subspectrum increased from 22 to 24 T. The behavior of nanocrystalline alloys under weak external magnetic field was analyzed within the three-level relaxation model of magnetic dynamics in an assembly of single-domain particles.

  4. Large-scale geometry and temporal variability of the Martian external magnetic field

    NASA Astrophysics Data System (ADS)

    Mittelholz, A.; Johnson, C. L.; Langlais, B.

    2014-12-01

    The martian magnetic field is unique among the terrestrial planets, as it results from the interaction of fields caused by crustal remnant magnetization and a planetary ionosphere with the solar wind and the interplanetary magnetic field. Internal fields of crustal origin have been subject to extensive studies, whereas the focus of our work deals with average spatial structure and time variability in the martian external magnetic field. We use the Mars Global Surveyor (MGS) vector magnetic field data to investigate the large-scale geometry and magnitude of such external fields. We analyze the day-time and night-time magnetic signature for the duration of the MGS mission in mapping orbit (2000-2006). We use along-track vector field measurements to estimate the day-time and night-time external fields after the subtraction of predicted crustal magnetic fields at spacecraft altitudes. We also examine day/night differences (i.e., the daily variation) in external fields; these are independent of crustal fields. Because the external fields are modified by the crustal fields, we investigate their structure as a function of latitude in the local time frame and as a function of both latitude and longitude in the body-fixed frame. In the body-fixed-frame BΘis generally dominant in magnitude with a day/night variation described to first order by a zonal degree-2 spherical harmonic structure. Br is strongly correlated with the crustal magnetic field. BΦ shows variable spatial behaviour during both night and day. Seasonal variations are observed as stronger average magnetic fields in the hemisphere pointing towards the sun. Additional shorter time scale variations in the global external field structure are observed.

  5. dc and ac magnetic properties of thin-walled Nb cylinders with and without a row of antidots.

    PubMed

    Tsindlekht, M I; Genkin, V M; Felner, I; Zeides, F; Katz, N; Gazi, Š; Chromik, Š; Dobrovolskiy, O V; Sachser, R; Huth, M

    2016-06-01

    dc and ac magnetic properties of two thin-walled superconducting Nb cylinders with a rectangular cross-section are reported. Magnetization curves and the ac response were studied on as-prepared and patterned samples in magnetic fields parallel to the cylinder axis. A row of micron-sized antidots (holes) was made in the film along the cylinder axis. Avalanche-like jumps of the magnetization are observed for both samples at low temperatures for magnetic fields not only above H c1, but in fields lower than H c1 in the vortex-free region. The positions of the jumps are not reproducible and they change from one experiment to another, resembling vortex lattice instabilities usually observed for magnetic fields larger than H c1. At temperatures above [Formula: see text] and [Formula: see text] the magnetization curves become smooth for the patterned and the as-prepared samples, respectively. The magnetization curve of a reference planar Nb film in the parallel field geometry does not exhibit jumps in the entire range of accessible temperatures. The ac response was measured in constant and swept dc magnetic field modes. Experiment shows that ac losses at low magnetic fields in a swept field mode are smaller for the patterned sample. For both samples the shapes of the field dependences of losses and the amplitude of the third harmonic are the same in constant and swept field near H c3. This similarity does not exist at low fields in a swept mode. PMID:27143621

  6. Holographic ρ mesons in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Callebaut, N.; Dudal, D.; Verschelde, H.

    2013-03-01

    We study the ρ meson in a uniform magnetic field eB using a holographic QCD-model, more specifically a D4/D8/overline{D8} brane setup in the confinement phase at zero temperature with two quenched flavours. The parameters of the model are fixed by matching to corresponding dual field theory parameters at zero magnetic field. We show that the up- and down-flavour branes respond differently to the presence of the magnetic field in the dual QCD-like theory, as expected because of the different electromagnetic charge carried by up- and down-quark. We discuss how to recover the Landau levels, indicating an instability of the QCD vacuum at eB=m_{ρ}^2 towards a phase where charged ρ mesons are condensed, as predicted by Chernodub using effective QCD-models. We improve on these existing effective QCD-model analyses by also taking into account the chiral magnetic catalysis effect, which tells us that the constituent quark masses rise with eB. This turns out to increase the value of the critical magnetic field for the onset of ρ meson condensation to eB≈ 1.1m_{ρ}^2≈ 0.67Ge{{V}^2} . We briefly discuss the influence of pions, which turn out to be irrelevant for the condensation in the approximation made.

  7. Magnetic nanoparticle thermometer: an investigation of minimum error transmission path and AC bias error.

    PubMed

    Du, Zhongzhou; Su, Rijian; Liu, Wenzhong; Huang, Zhixing

    2015-01-01

    The signal transmission module of a magnetic nanoparticle thermometer (MNPT) was established in this study to analyze the error sources introduced during the signal flow in the hardware system. The underlying error sources that significantly affected the precision of the MNPT were determined through mathematical modeling and simulation. A transfer module path with the minimum error in the hardware system was then proposed through the analysis of the variations of the system error caused by the significant error sources when the signal flew through the signal transmission module. In addition, a system parameter, named the signal-to-AC bias ratio (i.e., the ratio between the signal and AC bias), was identified as a direct determinant of the precision of the measured temperature. The temperature error was below 0.1 K when the signal-to-AC bias ratio was higher than 80 dB, and other system errors were not considered. The temperature error was below 0.1 K in the experiments with a commercial magnetic fluid (Sample SOR-10, Ocean Nanotechnology, Springdale, AR, USA) when the hardware system of the MNPT was designed with the aforementioned method. PMID:25875188

  8. Magnetic Nanoparticle Thermometer: An Investigation of Minimum Error Transmission Path and AC Bias Error

    PubMed Central

    Du, Zhongzhou; Su, Rijian; Liu, Wenzhong; Huang, Zhixing

    2015-01-01

    The signal transmission module of a magnetic nanoparticle thermometer (MNPT) was established in this study to analyze the error sources introduced during the signal flow in the hardware system. The underlying error sources that significantly affected the precision of the MNPT were determined through mathematical modeling and simulation. A transfer module path with the minimum error in the hardware system was then proposed through the analysis of the variations of the system error caused by the significant error sources when the signal flew through the signal transmission module. In addition, a system parameter, named the signal-to-AC bias ratio (i.e., the ratio between the signal and AC bias), was identified as a direct determinant of the precision of the measured temperature. The temperature error was below 0.1 K when the signal-to-AC bias ratio was higher than 80 dB, and other system errors were not considered. The temperature error was below 0.1 K in the experiments with a commercial magnetic fluid (Sample SOR-10, Ocean Nanotechnology, Springdale, AR, USA) when the hardware system of the MNPT was designed with the aforementioned method. PMID:25875188

  9. The external magnetic field created by the superposition of identical parallel finite solenoids

    NASA Astrophysics Data System (ADS)

    Lim, Melody Xuan; Greenside, Henry

    2016-08-01

    We use superposition and numerical methods to show that the external magnetic field generated by parallel identical solenoids can be nearly uniform and substantial, even when the solenoids have lengths that are large compared to their radii. We examine both a ring of solenoids and a large hexagonal array of solenoids. In both cases, we discuss how the magnitude and uniformity of the external field depend on the length of and the spacing between the solenoids. We also discuss some novel properties of a single solenoid, e.g., that even for short solenoids the energy stored in the internal magnetic field exceeds the energy stored in the spatially infinite external magnetic field. These results should be broadly interesting to undergraduates learning about electricity and magnetism.

  10. Observation of Landau levels on nitrogen-doped flat graphite surfaces without external magnetic fields

    NASA Astrophysics Data System (ADS)

    Kondo, Takahiro; Guo, Donghui; Shikano, Taishi; Suzuki, Tetsuya; Sakurai, Masataka; Okada, Susumu; Nakamura, Junji

    2015-11-01

    Under perpendicular external magnetic fields, two-dimensional carriers exhibit Landau levels (LLs). However, it has recently been reported that LLs have been observed on graphene and graphite surfaces without external magnetic fields being applied. These anomalous LLs have been ascribed primarily to a strain of graphene sheets, leading to in-plane hopping modulation of electrons. Here, we report the observation of the LLs of massive Dirac fermions on atomically flat areas of a nitrogen-doped graphite surface in the absence of external magnetic fields. The corresponding magnetic fields were estimated to be as much as approximately 100 T. The generation of the LLs at the area with negligible strain can be explained by inequivalent hopping of π electrons that takes place at the perimeter of high-potential domains surrounded by positively charged substituted graphitic-nitrogen atoms.

  11. Observation of Landau levels on nitrogen-doped flat graphite surfaces without external magnetic fields

    PubMed Central

    Kondo, Takahiro; Guo, Donghui; Shikano, Taishi; Suzuki, Tetsuya; Sakurai, Masataka; Okada, Susumu; Nakamura, Junji

    2015-01-01

    Under perpendicular external magnetic fields, two-dimensional carriers exhibit Landau levels (LLs). However, it has recently been reported that LLs have been observed on graphene and graphite surfaces without external magnetic fields being applied. These anomalous LLs have been ascribed primarily to a strain of graphene sheets, leading to in-plane hopping modulation of electrons. Here, we report the observation of the LLs of massive Dirac fermions on atomically flat areas of a nitrogen-doped graphite surface in the absence of external magnetic fields. The corresponding magnetic fields were estimated to be as much as approximately 100 T. The generation of the LLs at the area with negligible strain can be explained by inequivalent hopping of π electrons that takes place at the perimeter of high-potential domains surrounded by positively charged substituted graphitic-nitrogen atoms. PMID:26549618

  12. On Stellar Wind Bow Shocks with External Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Wilkin, Francis P.

    2016-06-01

    Stellar wind bow shocks have been seen driven by stars of many types, from O to AGB stars as well as pulsars. Recent simulations (e.g. van Marle et al. 2014) have considered the bubble created by a stellar wind of a stationary star in a region of constant magnetic field. By applying a thin-shell formalism, I consider the problem of a stellar wind from a star moving supersonically with respect to a magnetized medium. The properties of the resulting shell are derived, and limitations to the application of the resulting solution are discussed.

  13. External Horizontally Uniform Magnetic Field Applied to Steel Solidification

    NASA Astrophysics Data System (ADS)

    Mechighel, Farid; Kadja, Mahfoud

    Based on continuum model, a mathematical model for convection flow during directional solidification of steel, Fe-0.42wt%C, in an applied magnetic field is presented. The model includes mass, momentum, energy, species and electrical potential conservation equations. The geometry under study is rectangular. The permeability in the mushy zone is treated by means of the Blake-Kozeny equation. The system of equation has been discretized by means of Finite volume method. For solution of discretized equations SIMPLER Algorithm is used. The results show the strong effect of the magnetic field on the solidification process.

  14. Preparation of iron oxide nanoparticles by laser ablation in DMF under effect of external magnetic field

    NASA Astrophysics Data System (ADS)

    Ismail, Raid A.; Sulaiman, Ghassan M.; Abdulrahman, Safa A.

    2016-05-01

    We have studied the effect of applying an external magnetic field on the characteristics of iron oxide (IO) nanoparticles (NPs) synthesized by pulsed laser ablation in dimethylformamide (DMF). The NPs synthesized with and without applying of magnetic field were characterized by Fourier transformation infrared spectroscopy (FT-IR), UV-Vis absorption, scanning electron microscope (SEM), atomic force microscope (AFM), and X-ray diffraction (XRD). SEM results confirmed that the particle size was decreased after applying magnetic field.

  15. Orientational dynamics in magnetic fluids under strong coupling of external and internal relaxations

    NASA Astrophysics Data System (ADS)

    Raikher, Yu. L.; Stepanov, V. I.; Bacri, J. C.; Perzynski, R.

    2005-03-01

    For the geometry of crossed magnetic fields—one constant and one oscillating—a kinetic model for the field-induced birefringence of a ferrofluid, which allows for the internal and external magnetic relaxations in colloidal particles, is constructed. Using it to interpret the Argand diagrams, one gets an opportunity to analyze the effect of coherent relaxation: the case of exact coincidence of the diffusion rates of the particle magnetic moment.

  16. The effect of surface grain reversal on the AC losses of sintered Nd-Fe-B permanent magnets

    NASA Astrophysics Data System (ADS)

    Moore, Martina; Roth, Stefan; Gebert, Annett; Schultz, Ludwig; Gutfleisch, Oliver

    2015-02-01

    Sintered Nd-Fe-B magnets are exposed to AC magnetic fields in many applications, e.g. in permanent magnet electric motors. We have measured the AC losses of sintered Nd-Fe-B magnets in a closed circuit arrangement using AC fields with root mean square-values up to 80 mT (peak amplitude 113 mT) over the frequency range 50 to 1000 Hz. Two magnet grades with different dysprosium content were investigated. Around the remanence point the low grade material (1.7 wt% Dy) showed significant hysteresis losses; whereas the losses in the high grade material (8.9 wt% Dy) were dominated by classical eddy currents. Kerr microscopy images revealed that the hysteresis losses measured for the low grade magnet can be mainly ascribed to grains at the sample surface with multiple domains. This was further confirmed when the high grade material was subsequently exposed to DC and AC magnetic fields. Here a larger number of surface grains with multiple domains are also present once the step in the demagnetization curve attributed to the surface grain reversal is reached and a rise in the measured hysteresis losses is evident. If in the low grade material the operating point is slightly offset from the remanence point, such that zero field is not bypassed, its AC losses can also be fairly well described with classical eddy current theory.

  17. Can commercial ferrofluids be exploited in AC magnetic hyperthermia treatment to address diverse biomedical aspects?

    NASA Astrophysics Data System (ADS)

    Angelakeris, M.; Li, Zi-An; Sakellari, D.; Simeonidis, K.; Spasova, M.; Farle, M.

    2014-07-01

    Multifunctional magnetic nanoparticles are considered as promising candidates for various applications combining diagnosis, imaging and therapy. In the present work, we elaborate on the commercial colloidal solution "FluidMAG" (from Chemicell GmbH) as a possible candidate for magnetic hyperthermia application. The current product is a dispersion of magnetite nanoparticles employed for purification or separation of biotinylated biomolecules from different sources (e.g. blood). Transmission Electron Microscopy showed that the NPs have a spherical shape with mean diameter of 12.3 nm (± 20%), and SQUID magnetometry revealed their superparamagnetic character. Our promising results of the AC hyperthermia efficiency of "FluidMAG" suggest that with the appropriate manipulation it can also be exploited as magnetic hyperthermia agent.

  18. Role of external magnetic field and current closure in the force balance mechanism of a magnetically stabilized plasma torch

    NASA Astrophysics Data System (ADS)

    G, Ravi; Goyal, Vidhi

    2012-10-01

    Experimental investigations on the role of applied external magnetic field and return current closure in the force balance mechanism of a plasma torch are reported. The plasma torch is of low power and has wall, gas and magnetic stabilization mechanisms incorporated in it. Gas flow is divided into two parts: axial-central and peripheral-shroud, applied magnetic field is axial and return current is co-axial. Results indicate that application of large external magnetic field gives rise to not only J x B force but also, coupled with gas flow, to a new drag-cum-centrifugal force that acts on the plasma arc root and column. The magnetic field also plays a role in the return current closure dynamics and thus in the overall force balance mechanism. This in turn affects the electro-thermal efficiency of the plasma torch. Detailed experimental results, analytical calculations and physical model representing the processes will be presented and discussed.

  19. The effect of external magnetic fields on the pore structure of polyurethane foams loaded with magnetic microparticles

    NASA Astrophysics Data System (ADS)

    Schümann, M.; Seelig, N.; Odenbach, S.

    2015-10-01

    Elastic matrices loaded with magnetic microparticles are a new kind of magnetic hybrid material gaining a lot of scientific interest during the last few years. The central advantage of those materials is given by the possibility to control the mechanical properties by external stimuli, in this case external magnetic fields. Due to their extraordinary elastic properties, polyurethane foams are a promising matrix material for a new approach to synthesize such magnetic hybrid materials. A key to a deeper understanding of this new material is the investigation on how the inner structure of the hybrid material is controllable by the application of an external magnetic field during the polymerization. This paper presents a convenient method for analysis of structural changes of magnetically influenced particle loaded polyurethane foams. The geometry and size of up to 40 000 individual pores was evaluated by means of x-ray microtomography and digital image processing. A modest impact of the magnetic field on the pore structure was found with the utilized foam material, proving the convenient applicability of this method for future investigation with magnetic hybrid foams.

  20. Coexistence of superconductivity and magnetism in spin-fermion model of ferrimagnetic spinel in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Karchev, Naoum

    2015-04-01

    A two-sublattice spin-fermion model of ferrimagnetic spinel, with spin-1/2 itinerant electrons at the sublattice A site and spin-s localized electrons at the sublattice B site is considered. The exchange between itinerant and localized electrons is antiferromagnetic. As a result, the external magnetic field, applied along the magnetization of the localized electrons, compensates the Zeeman splitting due to the spin-fermion exchange and magnon-fermion interaction induces spin antiparallel p-wave superconductivity which coexists with magnetism. We have obtained five characteristic values of the applied field (in units of energy) H cr1 < H 3 < H 0 < H 4 < H cr2. At H 0 the external magnetic field compensates the Zeeman splitting. When H cr1 < H < H cr2 the spin antiparallel p-wave superconductivity with T 1u configuration coexists with magnetism. The superconductor-to-normal magnet transition at finite temperature is second order when H runs the interval (H_3,H_4) . It is an abrupt transition when H cr1 < H < H 3 or H 4 < H < H cr2. This is proved calculating the temperature dependence of the gap for three different values of the external magnetic field H cr1 < H < H 3, H 4 < H < H cr2 and H=H0 . In the first two cases the abrupt fall to zero of the gap at superconducting critical temperature shows that the superconductor-to-normal magnet transition is first order. The Hubbard term (Coulomb repulsion), in a weak-coupling regime, does not significantly affect the magnon-induced superconductivity. Relying on the above results one can formulate a recipe for preparing a superconductor from ferrimagnetic spinel: i) hydrostatic pressure above the critical value of insulator-metal transition; ii) external magnetic field along the sublattice magnetization with higher amplitude.

  1. Effect of ordered array of magnetic dots on the dynamics of Josephson vortices in stacked SNS Josephson junctions under DC and AC current

    NASA Astrophysics Data System (ADS)

    Berdiyorov, Golibjon R.; Savel'ev, Sergey; Kusmartsev, Feodor V.; Peeters, François M.

    2015-11-01

    We use the anisotropic time-dependent Ginzburg-Landau theory to investigate the effect of a square array of out-of-plane magnetic dots on the dynamics of Josephson vortices (fluxons) in artificial stacks of superconducting-normal-superconducting (SNS) Josephson junctions in the presence of external DC and AC currents. Periodic pinning due to the magnetic dots distorts the triangular lattice of fluxons and results in the appearance of commensurability features in the current-voltage characteristics of the system. For the larger values of the magnetization, additional peaks appear in the voltage-time characteristics of the system due to the creation and annihilation of vortex-antivortex pairs. Peculiar changes in the response of the system to the applied current is found resulting in a "superradiant" vortex-flow state at large current values, where a rectangular lattice of moving vortices is formed. Synchronizing the motion of fluxons by adding a small ac component to the biasing dc current is realized. However, we found that synchronization becomes difficult for large magnetization of the dots due to the formation of vortex-antivortex pairs.

  2. Earth's external magnetic fields at low orbital altitudes

    NASA Technical Reports Server (NTRS)

    Klumpar, D. M.

    1990-01-01

    Under our Jun. 1987 proposal, Magnetic Signatures of Near-Earth Distributed Currents, we proposed to render operational a modeling procedure that had been previously developed to compute the magnetic effects of distributed currents flowing in the magnetosphere-ionosphere system. After adaptation of the software to our computing environment we would apply the model to low altitude satellite orbits and would utilize the MAGSAT data suite to guide the analysis. During the first year, basic computer codes to run model systems of Birkeland and ionospheric currents and several graphical output routines were made operational on a VAX 780 in our research facility. Software performance was evaluated using an input matchstick ionospheric current array, field aligned currents were calculated and magnetic perturbations along hypothetical satellite orbits were calculated. The basic operation of the model was verified. Software routines to analyze and display MAGSAT satellite data in terms of deviations with respect to the earth's internal field were also made operational during the first year effort. The complete set of MAGSAT data to be used for evaluation of the models was received at the end of the first year. A detailed annual report in May 1989 described these first year activities completely. That first annual report is included by reference in this final report. This document summarizes our additional activities during the second year of effort and describes the modeling software, its operation, and includes as an attachment the deliverable computer software specified under the contract.

  3. Magnetic Driving Flowerlike Soft Platform: Biomimetic Fabrication and External Regulation.

    PubMed

    Gao, Wei; Wang, Lanlan; Wang, Xingzhe; Liu, Hongzhong

    2016-06-01

    Nature-inspired actuators that can be driven by various stimuli are an emerging application in mobile microrobotics and microfluidics. In this study, a soft and multiple-environment-adaptive robotic platform with ferromagnetic particles impregnated in silicon-based polymer is adopted to fabricate microrobots for minimally invasive locomotion and control interaction with their environment. As an intelligent structure of platform, the change of its bending, deformation, and flapping displacement is rapid, reversible, and continuously controllable with sweeping and multicycle magnetic actuation. The bending angle of the soft platform (0.2 mm in thickness and 8.5 mm in length) can be deflected up to almost 90° within 2.7 s. Experiments demonstrated that the flexible platform of human skin-like material in various shapes, that is, flowerlike shapes, can transport a cargo to targeted area in air and a variety of liquids. It indicates excellent magnetic-actuation ability and good controllability. The results may be helpful in developing a magnetic-driven carrying platform, which can be operated like a human finger to manipulate biological objects such as single cells, microbeads, or embryos. Especially, it is likely to be used in harsh chemical and physical circumstances. PMID:27182884

  4. AC transport in p-Ge/GeSi quantum well in high magnetic fields

    SciTech Connect

    Drichko, I. L.; Malysh, V. A.; Smirnov, I. Yu.; Golub, L. E.; Tarasenko, S. A.; Suslov, A. V.; Mironov, O. A.; Kummer, M.; Känel, H. von

    2014-08-20

    The contactless surface acoustic wave technique is implemented to probe the high-frequency conductivity of a high-mobility p-Ge/GeSi quantum well structure in the regime of integer quantum Hall effect (IQHE) at temperatures 0.3–5.8 K and magnetic fields up to 18 T. It is shown that, in the IQHE regime at the minima of conductivity, holes are localized and ac conductivity is of hopping nature and can be described within the “two-site” model. The analysis of the temperature and magnetic-field-orientation dependence of the ac conductivity at odd filing factors enables us to determine the effective hole g-factor, |g{sub zz}|≈4.5. It is shown that the in-plane component of the magnetic field leads to a decrease in the g-factor as well as increase in the cyclotron mass, which is explained by orbital effects in the complex valence band of germanium.

  5. Sensitivity of detachment extent to magnetic configuration and external parameters

    NASA Astrophysics Data System (ADS)

    Lipschultz, Bruce; Parra, Felix I.; Hutchinson, Ian H.

    2016-05-01

    Divertor detachment may be essential to reduce heat loads to magnetic fusion tokamak reactor divertor surfaces. Yet in experiments it is difficult to control the extent of the detached, low pressure, plasma region. At maximum extent the front edge of the detached region reaches the X-point and can lead to degradation of core plasma properties. We define the ‘detachment window’ in a given position control variable C (for example, the upstream plasma density) as the range in C within which the front location can be stably held at any position from the target to the X-point; increased detachment window corresponds to better control. We extend a 1D analytic model [1] to determine the detachment window for the following control variables: the upstream plasma density, the impurity concentration and the power entering the scrape-off layer (SOL). We find that variations in magnetic configuration can have strong effects; increasing the ratio of the total magnetic field at the X-point to that at the target, {{B}×}/{{B}t} , (total flux expansion, as in the super-x divertor configuration) strongly increases the detachment window for all control variables studied, thus strongly improving detachment front control and the capability of the divertor plasma to passively accommodate transients while still staying detached. Increasing flux tube length and thus volume in the divertor, through poloidal flux expansion (as in the snowflake or x-divertor configurations) or length of the divertor, also increases the detachment window, but less than the total flux expansion does. The sensitivity of the detachment front location, z h , to each control variable, C, defined as \\partial {{z}h}/\\partial C , depends on the magnetic configuration. The size of the radiating volume and the total divertor radiation increase \\propto {{≤ft({{B}×}/{{B}t}\\right)}2} and \\propto {{B}×}/{{B}t} , respectively, but not by increasing divertor poloidal flux expansion or field line length. We

  6. Controlling the magnetic susceptibility in an artificial elliptical quantum ring by magnetic flux and external Rashba effect

    SciTech Connect

    Omidi, Mahboubeh Faizabadi, Edris

    2015-03-21

    Magnetic susceptibility is investigated in a man-made elliptical quantum ring in the presence of Rashba spin-orbit interactions and the magnetic flux. It is shown that magnetic susceptibility as a function of magnetic flux changes between negative and positive signs periodically. The periodicity of the Aharonov-Bohm oscillations depends on the geometry of the region where magnetic field is applied, the eccentricity, and number of sites in each chain ring (the elliptical ring is composed of chain rings). The magnetic susceptibility sign can be reversed by tuning the Rashba spin-orbit strength as well. Both the magnetic susceptibility strength and sign can be controlled via external spin-orbit interactions, which can be exploited in spintronics and nanoelectronics.

  7. Design of a novel phase-decoupling permanent magnet brushless ac motor

    NASA Astrophysics Data System (ADS)

    Cui, Wei; Chau, K. T.; Jiang, J. Z.; Fan, Ying

    2005-05-01

    This paper presents a phase-decoupling permanent magnet brushless ac motor which can offer better controllability, faster response, and smoother torque than its counterparts. The key is due to its different motor configuration and simple scalar control. The motor configuration is so unique that it inherently offers the features of phase decoupling, flux focusing, and flux shaping, hence achieving independent phase control, fast response, and smooth torque. The scalar control is fundamentally different from the complicated vector control. It can achieve direct torque control through independent control of the phase currents. The proposed motor is prototyped and experimentally verified.

  8. An adaptive fuzzy controller for permanent-magnet AC servo drives

    SciTech Connect

    Le-Huy, H.

    1995-12-31

    This paper presents a theoretical study on a model-reference adaptive fuzzy logic controller for vector-controlled permanent-magnet ac servo drives. In the proposed system, fuzzy logic is used to implement the direct controller as well as the adaptation mechanism. The operation of the direct fuzzy controller and the fuzzy logic based adaptation mechanism is studied. The control performance of the adaptive fuzzy controller is evaluated by simulation for various operating conditions. The results are compared with that provided by a non-adaptive fuzzy controller. The implementation of proposed adaptive fuzzy controller is discussed.

  9. Spin superconductivity and ac-Josephson effect in Graphene system under strong magnetic field

    NASA Astrophysics Data System (ADS)

    Liu, Haiwen; Jiang, Hua; Sun, Qing-Feng; Xie, X. C.; Collaborative Innovation Center of Quantum Matter, Beijing, China Collaboration

    We study the spin superconductivity in Graphene system under strong magnetic field. From the microscopically Gor'kov method combined with the Aharonov-Casher effect, we derive the effective Landau-Ginzburg free energy and analyze the time evolution of order parameter, which is confirmed to be the off-diagonal long range order. Meanwhile, we compare the ground state of spin superconductivity to the canted-antiferromagnetic state, and demonstrate the equivalence between these two states. Moreover, we give out the pseudo-field flux quantization condition of spin supercurrent, and propose an experimental measurable ac-Josephson effect of spin superconductivity in this system.

  10. Tuning the colloidal crystal structure of magnetic particles by external field.

    PubMed

    Pal, Antara; Malik, Vikash; He, Le; Erné, Ben H; Yin, Yadong; Kegel, Willem K; Petukhov, Andrei V

    2015-02-01

    Manipulation of the self-assembly of magnetic colloidal particles by an externally applied magnetic field paves a way toward developing novel stimuli responsive photonic structures. Using microradian X-ray scattering technique we have investigated the different crystal structures exhibited by self-assembly of core-shell magnetite/silica nanoparticles. An external magnetic field was employed to tune the colloidal crystallization. We find that the equilibrium structure in absence of the field is random hexagonal close-packed (RHCP) one. External field drives the self-assembly toward a body-centered tetragonal (BCT) structure. Our findings are in good agreement with simulation results on the assembly of these particles. PMID:25510837

  11. The Impact of Century-Scale Changes in the Core Magnetic Field on External Magnetic Field Contributions

    NASA Astrophysics Data System (ADS)

    Cnossen, Ingrid

    2016-08-01

    The Earth's internal magnetic field controls to a degree the strength, geographic positioning, and structure of currents flowing in the ionosphere and magnetosphere, which produce their own (external) magnetic fields. The secular variation of the Earth's internal magnetic field can therefore lead to long-term changes in the externally produced magnetic field as well. Here we will examine this more closely. First, we obtain scaling relations to describe how the strength of magnetic perturbations associated with various different current systems in the ionosphere and magnetosphere depends on the internal magnetic field intensity. Second, we discuss how changes in the orientation of a simple dipolar magnetic field will affect the current systems. Third, we use model simulations to study how actual changes in the Earth's internal magnetic field between 1908 and 2008 have affected some of the relevant current systems. The influence of the internal magnetic field on low- to mid-latitude currents in the ionosphere is relatively well understood, while the effects on high-latitude current systems and currents in the magnetosphere still pose considerable challenges.

  12. Externally controlled local magnetic field in a conducting mesoscopic ring coupled to a quantum wire

    SciTech Connect

    Maiti, Santanu K.

    2015-01-14

    In the present work, the possibility of regulating local magnetic field in a quantum ring is investigated theoretically. The ring is coupled to a quantum wire and subjected to an in-plane electric field. Under a finite bias voltage across the wire a net circulating current is established in the ring which produces a strong magnetic field at its centre. This magnetic field can be tuned externally in a wide range by regulating the in-plane electric field, and thus, our present system can be utilized to control magnetic field at a specific region. The feasibility of this quantum system in designing spin-based quantum devices is also analyzed.

  13. Dynamic melting and impurity particle tracking in continuously adjustable AC magnetic field

    NASA Astrophysics Data System (ADS)

    Bojarevics, V.; Pericleous, K.

    2016-07-01

    The analysis of semi-levitation melting is extended to account for the presence of particles (impurities, broken metal dendrite agglomerates, bubbles) during the full melting cycle simulated numerically using the pseudo-spectral schemes. The AC coil is dynamically moving with the melt front progress, while the generated Joule heat serves to enhance the melting rate. The electromagnetic force is decomposed into the time average and the oscillating parts. The time average effects on the particle transport are investigated previously using approximations derived for a locally uniform magnetic field. This paper presents expressions for the skin-layer type of the AC force containing also the pulsating part which contributes to the particle drag by the ‘history’ and ‘added mass’ contributions. The intense turbulence in the bulk of molten metal additionally contributes to the particle dispersion. The paper attempts to demonstrate the importance of each of the mentioned effects onto the particle transport during the melting until the final pouring stage. The method could be extended to similar AC field controlled melting/solidification processes.

  14. Output microwave radiation power of low-voltage vircator with external inhomogeneous magnetic field

    NASA Astrophysics Data System (ADS)

    Kurkin, S. A.; Koronovskii, A. A.; Hramov, A. E.

    2011-04-01

    Dependence of the power of a broadband microwave radiation generated by a low-voltage oscillator with virtual cathode (vircator) on the parameters of an external inhomogeneous magnetic field has been studied by numerical simulations using a two-dimensional model. It is established that there are optimum parameters of the generator (configuration of the external magnetic field, electron beam current) for which the output radiation power is maximum. A relationship between the optimum conditions of virtual cathode formation in the electron beam and the microwave generation regime is established.

  15. Chaotic signal generation in low-voltage vircator with electron source shielded from external magnetic field

    NASA Astrophysics Data System (ADS)

    Kurkin, S. A.; Hramov, A. E.; Koronovskii, A. A.

    2011-02-01

    The effect of shielding an electron source from a homogeneous external magnetic field of the drift chamber on the nonlinear dynamics of the electron beam with a virtual cathode (VC) and on the characteristics of output microwave radiation in a low-voltage vircator have been numerically simulated within the framework of a two-dimensional model. It is established that the increased degree of shielding of the electron source from the external magnetic field leads to the complication of the VC dynamics in the system and the corresponding chaotization of the output microwave radiation. Physical processes that account for the observed effect of shielding are analyzed.

  16. Simulation study of enhancing laser-driven multi-keV line-radiation through application of external magnetic fields

    NASA Astrophysics Data System (ADS)

    Kemp, G. Elijah; Colvin, J. D.; Fournier, K. B.; May, M. J.; Barrios, M. A.; Patel, M. V.; Koning, J. M.; Scott, H. A.; Marinak, M. M.

    2015-11-01

    Laser-driven, spectrally tailored, high-flux x-ray sources have been developed over the past decade for testing the radiation hardness of materials used in various civilian, space and military applications. The optimal electron temperatures for these x-ray sources occur around twice the desired photon energy. At the National Ignition Facility (NIF) laser, the available energy can produce plasmas with ~ 10keV electron temperatures which result in highly-efficient ~ 5keV radiation but less than optimal emission from the > 10keV sources. In this work, we present a possible venue for enhancing multi-keV x-ray emission on existing laser platforms through the application of an external magnetic field. Preliminary radiation-hydrodynamics calculations with Hydra suggest as much as 2 - 14 × increases in laser-to-x-ray conversion efficiency for 22 - 68keV K-shell sources are possible on the NIF laser - without any changes in laser-drive conditions - through the application of an external axial 50 T field. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

  17. Bucking Coil Efficiency Correction for 5'' PMT Exposed to an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Llodra, Anthony; Reinhold, Joerg

    2014-03-01

    This research was conducted in support of the Hall C upgrade activities at Thomas Jefferson National Accelerator Facility (JLab). We propose to employ bucking coils in order to maximize the collection efficiency of the 5'' PMTs installed on the Cherenkov detector, which could potentially be exposed to external magnetic field produced by the Super Conducting Super High Momentum Spectrometer (SHMS) magnet. In this research project a 5'' PMT was placed in a light tight cylinder with a fiber optic cable. The cylinder was centered within a set of Helmholtz coils to produce a constant external magnetic field. Furthermore, the cylinder was wrapped with 20 coils of standard 12 gauge cable to act as the bucking coil. With the intensity of the LED source, and the magnitude of the external magnetic field fixed at a carefully determined value, data was taken to determine if the collection efficiency of the PMT was indeed affected. With a decrease in collection efficiency confirmed, further data were taken. A range of current (0-6 A) was applied to the bucking coils, while ADC spectra were analyzed in intervals of 0.25 A. The data indicated that in an external magnetic field of approximately 3 Gauss, the 5'' PMT collection efficiency is maximized with the bucking coil current set to approximately 3.5 A. Thus, the data conclusively indicates that the bucking coil system will indeed maximize the collection efficiency of the 5'' PMT. Florida International University.

  18. Coherence-population-trapping transients induced by an ac magnetic field

    NASA Astrophysics Data System (ADS)

    Margalit, L.; Rosenbluh, M.; Wilson-Gordon, A. D.

    2012-06-01

    Coherent-population-trapping transients induced by an ac magnetic field are investigated theoretically for a realistic three-level Λ system in the D1 line of 87Rb. The contributions to the transient probe absorption from the various subsystems that compose the realistic atomic system are examined and the absorption of each Λ subsystem is compared to that of a simple Λ system. The population redistribution due to optical pumping is shown to be the dominant cause of the difference between the contributions of the various subsystems to the oscillatory character of the probe absorption. We also discuss the series of transients that reappear every half-cycle time of a modulated magnetic field when the system is in two-photon resonance, and we study the transient behavior as a function of the probe detuning. The effect of a buffer gas on the amplitude and shape of the transients is considered.

  19. Test Results of the AC Field Measurements of Fermilab Booster Corrector Magnets

    SciTech Connect

    DiMarco, E.Joseph; Harding, D.J.; Kashikhin, V.S.; Kotelnikov, S.K.; Lamm, M.J.; Makulski, A.; Nehring, R.; Orris, D.F.; Schlabach, P.; Sylvester, C.; Tartaglia, Michael Albert; /Fermilab

    2008-06-25

    Multi-element corrector magnets are being produced at Fermilab that enable correction of orbits and tunes through the entire cycle of the Booster, not just at injection. The corrector package includes six different corrector elements--normal and skew orientations of dipole, quadrupole, and sextupole--each independently powered. The magnets have been tested during typical AC ramping cycles at 15Hz using a fixed coil system to measure the dynamic field strength and field quality. The fixed coil is comprised of an array of inductive pick-up coils around the perimeter of a cylinder which are sampled simultaneously at 100 kHz with 24-bit ADC's. The performance of the measurement system and a summary of the field results are presented and discussed.

  20. Influence of the ac magnetic field frequency on the magnetoimpedance of amorphous wire

    NASA Astrophysics Data System (ADS)

    Chen, A. P.; García, C.; Zhukov, A.; Domínguez, L.; Blanco, J. M.; González, J.

    2006-05-01

    Experimental and theoretical studies on the influence of ac magnetic field frequency on the axial diagonal (ζzz) and off-diagonal (ζphiz) components of the magnetoimpedance (MI) tensor in (Co0.94Fe0.06)72.5Si12.5B15 amorphous wires have been performed. The frequency (f) of an ac current flowing along the wire was varied from 1 to 20 MHz with the current amplitude less than 15 mA. In order to enhance the ζphiz component, the amorphous wire was submitted to torsion annealing for developing and preserving a helical magnetic anisotropy in the surface of the wire. The experimental measurements show that the value of the impedance is proportional to the square-root of the ac current frequency, \\sqrt f , in the vicinity of Hex < HK and this increase is due to the contribution of the resistance (real part of the impedance). The measurements also indicate that the peaks of the MI curve shift slightly towards higher field values with increasing f. In a theoretical study the magnetoimpedance expressions ζzz and ζphiz have been deduced using the Faraday law in combination with the solutions of the Maxwell and Landau-Lifshitz-Gilbert (LLG) equations. By analysing quantitatively the spectra of ζzz and ζphiz, the phenomenon of the shift in the peaks of the MI curve with f has been considered as a characteristic of the helical anisotropy in the domain structure of the wire surface.

  1. Creep Void Detection for Low Alloy Steel Using AC Magnetic Method

    SciTech Connect

    Shiwa, M.; Cheng, W.; Kume, R.

    2004-02-26

    Nondestructive detection of creep void was developed for low alloy steel by using AC magnetic method. Two types of 2.25Cr-1Mo steel specimens, base metal (BM) and simulated heat affected zone (HAZ) under aging and creep damage, were prepared for the tests. A differential type probe was used to detect AC magnetic signals. The exciting and detecting coils were coaxially arranged with a ferrite core. Signals were recorded using a 2-channel waveform recorder. The equivalent hysteresis loss (HL) was analyzed. It was observed that the HL of BM and HAZ changed in opposite direction, that is, HL of BM increased and HL of HAZ decreased with aging time. On the other hand, the HLs of both BM and HAZ decreased with creep time. The HL of creep samples was affected by both aging and stress-induced damage. In order to evaluate creep damage, stress-induced damage (SID) parameter was proposed to remove aging factor of materials from HL. Creep void were observed by scanning electron microscope (SEM) for all creep damage samples of SID value under 0.8.

  2. Magnetization and diamagnetism of a longitudinal autosoliton in p-InSb in an external longitudinal magnetic field

    NASA Astrophysics Data System (ADS)

    Kamilov, I. K.; Stepurenko, A. A.; Gummetov, A. E.

    2016-07-01

    It has been experimentally shown that a longitudinal thermal-diffusion autosoliton, which is generated in a nonequilibrium electron-hole plasma in p-InSb, in an external longitudinal magnetic field acquires diamagnetic properties. The results of the calculation and numerical estimates of the diamagnetism have been presented.

  3. Roles of effective helical ripple rates in nonlinear stability of externally induced magnetic islands

    SciTech Connect

    Nishimura, Seiya

    2015-02-15

    Magnetic islands are externally produced by resonant magnetic perturbations (RMPs) in toroidal plasmas. Spontaneous annihilation of RMP-induced magnetic islands called self-healing has been observed in helical systems. A possible mechanism of the self-healing is shielding of RMP penetration by helical ripple-induced neoclassical flows, which give rise to neoclassical viscous torques. In this study, effective helical ripple rates in multi-helicity helical systems are revisited, and a multi-helicity effect on the self-healing is investigated, based on a theoretical model of rotating magnetic islands. It is confirmed that effective helical ripple rates are sensitive to magnetic axis positions. It is newly found that self-healing thresholds also strongly depend on magnetic axis positions, which is due to dependence of neoclassical viscous torques on effective helical ripple rates.

  4. Dynamic model tracking design for low inertia, high speed permanent magnet ac motors.

    PubMed

    Stewart, P; Kadirkamanathan, V

    2004-01-01

    Permanent magnet ac (PMAC) motors have existed in various configurations for many years. The advent of rare-earth magnets and their associated highly elevated levels of magnetic flux makes the permanent magnet motor attractive for many high performance applications from computer disk drives to all electric racing cars. The use of batteries as a prime storage element carries a cost penalty in terms of the unladen weight of the vehicle. Minimizing this cost function requires the minimum electric motor size and weight to be specified, while still retaining acceptable levels of output torque. This tradeoff can be achieved by applying a technique known as flux weakening which will be investigated in this paper. The technique allows the speed range of a PMAC motor to be greatly increased, giving a constant power range of more than 4:1. A dynamic model reference controller is presented which has advantages in ease of implementation, and is particularly suited to dynamic low inertia applications such as clutchless gear changing in high performance electric vehicles. The benefits of this approach are to maximize the torque speed envelope of the motor, particularly advantageous when considering low inertia operation. The controller is examined experimentally, confirming the predicted performance. PMID:15000141

  5. Global-scale external magnetic fields at Mars from Mars Global Surveyor data

    NASA Astrophysics Data System (ADS)

    Mittelholz, A.; Johnson, C. L.

    2015-12-01

    The martian magnetic field is unique among those of the terrestrial planets. It is the net result of the interaction of the solar wind and interplanetary magnetic field (IMF) with crustal remnant magnetization and a planetary ionosphere. Internal fields of crustal origin have been the subject of extensive studies; the focus of our work is identification and characterization of contributions from external magnetic fields using the Mars Global Surveyor (MGS) vector magnetic field data. We investigate the magnitude, average spatial structure and temporal variability of the external magnetic field at the MGS mapping altitude of 400 km by first subtracting expected contributions from crustal fields using existing global crustal field models. We identify contributions to the residual dayside fields from two sources: the draped IMF and a source that we interpret to be of ionospheric origin. As observed in previous work, nightside external fields are minimal at mapping orbit altitudes. The IMF contribution changes polarity every 13 days due to the geometry of the heliospheric magnetic field and Mars' orbit. This allows us to calculate the amplitude of the IMF at mapping orbit altitudes. The ionospheric contribution results in a quasi-steady dayside signal in the MGS observations because of the limited local time sampling of the MGS mapping orbit. The ionospheric contribution can be isolated by averaging the external fields over timescales longer than several Carrington rotations, to average out the IMF contribution. We present a global average of the ionopsheric field for the duration of the mapping orbit (2000-2006) and analyze daytime and nightime fields separately. We show that some structure in the time-averaged ionospheric field is organized in the Mars body-fixed frame, due for example, to the influence of crustal fields. We also show that the ionospheric fields vary in amplitude and geometry with martian season. Broader local time coverage over a restricted latitude

  6. Thermodynamics of the Mn12-ac molecule in a skew magnetic field at T \\gtrsim 21 K

    NASA Astrophysics Data System (ADS)

    Rojas, Onofre; Thomaz, M. T.; Corrêa Silva, E. V.; de Souza, S. M.

    2009-01-01

    We derive the high-temperature expansion of the Helmholtz free energy of the quantum and classical models for the Mn12-ac molecule in the presence of a skew magnetic field, including the transverse term in the Hamiltonians, for T \\gtrsim 21 K. In this region of temperature, we show that the transverse term can give a measurable contribution to the x component of the magnetization. We obtain the specific heat per site of a powder sample of Mn12-ac under a constant magnetic field. For strong skew magnetic fields (h/D>1), the specific heat differs up to 20% from its value of a crystal sample under purely longitudinal magnetic fields. Finally, we obtain that in the limit T \\rightarrow \\infty , the values of the classical and quantum specific heat differ; in particular, for \\vec {h}= \\vec 0 this difference is 0.96%.

  7. Precision measurement of magnetic characteristics of an article with nullification of external magnetic fields

    NASA Technical Reports Server (NTRS)

    Honess, Shawn B. (Inventor); Narvaez, Pablo (Inventor); Mcauley, James M. (Inventor)

    1992-01-01

    An apparatus for characterizing the magnetic field of a device under test is discussed. The apparatus is comprised of five separate devices: (1) a device for nullifying the ambient magnetic fields in a test environment area with a constant applied magnetic field; (2) a device for rotating the device under test in the test environment area; (3) a device for sensing the magnetic field (to obtain a profile of the magnetic field) at a sensor location which is along the circumference of rotation; (4) a memory for storing the profiles; and (5) a processor coupled to the memory for characterizing the magnetic field of the device from the magnetic field profiles thus obtained.

  8. Colloidal Suspensions of Rodlike Nanocrystals and Magnetic Spheres under an External Magnetic Stimulus: Experiment and Molecular Dynamics Simulation.

    PubMed

    May, Kathrin; Eremin, Alexey; Stannarius, Ralf; Peroukidis, Stavros D; Klapp, Sabine H L; Klein, Susanne

    2016-05-24

    Using experiments and molecular dynamics simulations, we explore magnetic field-induced phase transformations in suspensions of nonmagnetic rodlike and magnetic sphere-shaped particles. We experimentally demonstrate that an external uniform magnetic field causes the formation of small, stable clusters of magnetic particles that, in turn, induce and control the orientational order of the nonmagnetic subphase. Optical birefringence was studied as a function of the magnetic field and the volume fractions of each particle type. Steric transfer of the orientational order was investigated by molecular dynamics (MD) simulations; the results are in qualitative agreement with the experimental observations. By reproducing the general experimental trends, the MD simulation offers a cohesive bottom-up interpretation of the physical behavior of such systems, and it can also be regarded as a guide for further experimental research. PMID:27119202

  9. Ground states of spin-2 condensates in an external magnetic field

    SciTech Connect

    Zheng, G.-P.; Tong, Y.-G.; Wang, F.-L.

    2010-06-15

    The possible ground states of spin-2 Bose-Einstein condensates in an external magnetic field are obtained analytically and classified systematically according to the population of the condensed atoms at the hyperfine sublevels. It is shown that the atoms can populate simultaneously at four hyperfine sublevels in a weak magnetic field with only the linear Zeeman energy, in contrast to that in a stronger magnetic field with the quadratic Zeeman energy, where condensed atoms can at most populate at three hyperfine sublevels in the ground states. Any spin configuration we obtained will give a closed subspace in the order parameter space of the condensates.

  10. Microwave complex conductivity of the YBCO thin films as a function of static external magnetic field

    NASA Astrophysics Data System (ADS)

    Krupka, J.; Judek, J.; Jastrzebski, C.; Ciuk, T.; Wosik, J.; Zdrojek, M.

    2014-03-01

    A sapphire rod resonator operating at microwave frequencies was used to determine the electric properties of 600 nm thick YBCO films in the superconducting state. The rigorous electromagnetic modelling was applied to transform the measured Q-factor and the resonant frequency to the complex conductivity of high accuracy, which was previously shown to describe the intrinsic properties of superconductor thin films in more precise manner than the complex impedance. Static external magnetic field induces typical transition to normal state due to introduction of magnetic vortices into the sample. Observed magnetic hysteresis has the origin in the strong temperature dependent pinning. Additional energy absorption at about 1.5 T was observed.

  11. Mass of Kerr-Newman black holes in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Astorino, M.; Compère, G.; Oliveri, R.; Vandevoorde, N.

    2016-07-01

    The explicit solution for a Kerr-Newman black hole immersed in an external magnetic field, sometimes called the Melvin-Kerr-Newman black hole, has been derived by Ernst and Wild in 1976. In this paper, we clarify the first law and Smarr formula for black holes in a magnetic field. We then define the unique mass which is integrable and reduces to the Kerr-Newman mass in the absence of magnetic field. This defines the thermodynamic potentials of the black hole. Quite strikingly, the mass coincides with the standard Christodoulou-Ruffini mass of a black hole as a function of the entropy, angular momentum and electric charge.

  12. An optimum design of implosion with external magnetic field for electron beam guiding in fast ignition

    NASA Astrophysics Data System (ADS)

    Nagatomo, H.; Johzaki, T.; Asahina, T.; Matsuo, K.; Sunahara, A.; Sakagami, H.; Sano, T.; Mima, K.; Morace, A.; Zhang, Z.; Fujioka, S.; Shigemori, K.; Shiraga, H.; FIREX project group

    2016-05-01

    Compression of solid spherical target under the strong external magnetic field is studied using two dimensional radiative magneto-hydrodynamic (MHD) simulation code for fast ignition. The simulation results show that a compression of a solid sphere target is stable, and it is possible to achieve a high areal density core plasma. Assuming the GXII scale laser, it will be ρR=60-80mg/cm2. Due to the magnetic diffusion in the solid target, the magnetic mirror ratio is less than 4, which does not reflect most of the hot electrons for heating core. These properties are preferable for fast ignition scheme.

  13. Electron beam guiding by external magnetic fields in imploded fuel plasma

    NASA Astrophysics Data System (ADS)

    Johzaki, T.; Sentoku, Y.; Nagatomo, H.; Sunahara, A.; Sakagami, H.; Fujioka, S.; Shiraga, H.; Endo, T.; FIREX project group

    2016-05-01

    For enhancing the core heating efficiency in fast ignition laser fusion, we proposed the fast electron beam by externally-applied the kilo-tesla (kT) class longitudinal magnetic field. We evaluated the imploded core and the magnetic field profiles formed through the implosion dynamics by resistive MHD radiation hydro code. Using those profiles, the guiding effect was evaluated by fast electron transport simulations, which shows that in addition to the feasible field configuration (moderate mirror ratio), the kT-class magnetic field is required at the fast electron generation point. In this case, the significant enhancement in heating efficiency is expected.

  14. dc and ac magnetic properties of thin-walled Nb cylinders with and without a row of antidots

    NASA Astrophysics Data System (ADS)

    Tsindlekht, M. I.; Genkin, V. M.; Felner, I.; Zeides, F.; Katz, N.; Gazi, Š.; Chromik, Š.; Dobrovolskiy, O. V.; Sachser, R.; Huth, M.

    2016-06-01

    dc and ac magnetic properties of two thin-walled superconducting Nb cylinders with a rectangular cross-section are reported. Magnetization curves and the ac response were studied on as-prepared and patterned samples in magnetic fields parallel to the cylinder axis. A row of micron-sized antidots (holes) was made in the film along the cylinder axis. Avalanche-like jumps of the magnetization are observed for both samples at low temperatures for magnetic fields not only above H c1, but in fields lower than H c1 in the vortex-free region. The positions of the jumps are not reproducible and they change from one experiment to another, resembling vortex lattice instabilities usually observed for magnetic fields larger than H c1. At temperatures above 0.66{{T}\\text{c}} and 0.78{{T}\\text{c}} the magnetization curves become smooth for the patterned and the as-prepared samples, respectively. The magnetization curve of a reference planar Nb film in the parallel field geometry does not exhibit jumps in the entire range of accessible temperatures. The ac response was measured in constant and swept dc magnetic field modes. Experiment shows that ac losses at low magnetic fields in a swept field mode are smaller for the patterned sample. For both samples the shapes of the field dependences of losses and the amplitude of the third harmonic are the same in constant and swept field near H c3. This similarity does not exist at low fields in a swept mode.

  15. Measurements on magnetized GdBCO pellets subjected to small transverse ac magnetic fields at very low frequency: Evidence for a slowdown of the magnetization decay

    NASA Astrophysics Data System (ADS)

    Fagnard, Jean-Francois; Kirsch, Sébastien; Morita, Mitsuru; Teshima, Hidekazu; Vanderheyden, Benoit; Vanderbemden, Philippe

    2015-05-01

    Due to their ability to trap large magnetic inductions, superconducting bulk materials can be used as powerful permanent magnets. The permanent magnetization of such materials, however, can be significantly affected by the application of several cycles of a transverse variable magnetic field. In this work, we study, at T = 77 K, the long term influence of transverse ac magnetic fields of small amplitudes (i.e. much smaller than the full penetration field) on the axial magnetization of a bulk single grain superconducting GdBCO pellet over a wide range of low frequencies (1 mHz-20 Hz). Thermocouples are placed against the pellet surface to probe possible self-heating of the material during the experiments. A high sensitivity cryogenic Hall probe is placed close to the surface to record the local magnetic induction normal to the surface. The results show first that, for a given number of applied triangular transverse cycles, higher values of dBapp/dt induce smaller magnetization decays. An important feature of practical interest is that, after a very large number of cycles which cause the loss of a substantial amount of magnetization (depending on the amplitude and the frequency of the field), the rate of the magnetization decay goes back to its initial value, corresponding to the relaxation of the superconducting currents due to flux creep only. In the amplitude and frequency range investigated, the thermocouples measurements and a 2D magneto-thermal modelling show no evidence of sufficient self-heating to affect the magnetization so that the effect of the transverse magnetic field cycles on the trapped magnetic moment is only attributed to a redistribution of superconducting currents in the volume of the sample and not to a thermal effect.

  16. First-principles study on magnetism of Ru monolayer under an external electric field

    NASA Astrophysics Data System (ADS)

    Kitaoka, Yukie; Imamura, Hiroshi

    Electric field control of magnetic properties such as magnetic moment and magnetic anisotropy has been attracted. For the 4 d TM films, on the other hand, it was recently reported that the ferromagnetism Pd thin-film is induced by application of an external electric field otherwise Pd thin-film shows paramagnetic. However, little attention has been paid to the magnetism of other 4 d TMs. Here, we investigate the magnetism of the free-standing Ru monolayer and that on MgO(001) substrate under an external electric field by using first-principles FLAPW method. We found that the free-standing Ru monolayer is ferromagnet with magnetic moment of 1.50 ¥muB /atom. The MA energy is 3.45 meV/atom, indicating perpendicular MA, at zero electric field (E=0) and increases up to 3.84 meV/atom by application of E=1 (V/¥AA). The Ru monolayer on MgO(001) substrate is also ferromagnet with magnetic moment of 0.89 ¥muB /atom. The MA energy is 1.49 meV/atom, indicating perpendicular MA, at E=0 and decreases to 1.33 meV/atom by application of E=1 (V/¥AA).

  17. Effect of buffer layer and external stress on magnetic properties of flexible FeGa films

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoshan; Zhan, Qingfeng; Dai, Guohong; Liu, Yiwei; Zuo, Zhenghu; Yang, Huali; Chen, Bin; Li, Run-Wei

    2013-05-01

    We systematically investigated the effect of a Ta buffer layer and external stress on the magnetic properties of magnetostrictive Fe81Ga19 films deposited on flexible polyethylene terephthalate (PET) substrates. The Ta buffer layers could effectively smoothen the rough surface of PET. As a result, the FeGa films grown on Ta buffer layers exhibit a weaker uniaxial magnetic anisotropy and lower coercivity, as compared to those films directly grown on PET substrates. By inward and outward bending the FeGa/Ta/PET samples, external in-plane compressive and tensile stresses were applied to the magnetic films. Due to the inverse magnetostrictive effect of FeGa, both the coercivity and squareness of hysteresis loops for FeGa/Ta films could be well tuned under various strains.

  18. Meg recordings of patients with CNS disorders before and after external magnetic stimulation.

    PubMed

    Anninos, P; Kotini, A; Anninou, N; Adamopoulos, A; Papastergiou, A; Tsagas, N

    2008-03-01

    Magnetoencephalographic (MEG) recordings of patients with CNS disorders were obtained using a whole-head 122-channel magnetometer SQUID and analyzed using Fourier statistical analysis. External transcranial magnetic stimulation in the order of pico Tesla (pTMS) was applied to the above patients with proper characteristics (magnetic intensity 1-7.5 pT; frequency: 8-13 Hz) which were obtained with MEG recordings prior to pTMS. The MEG recordings after the application of pTMS showed a rapid attenuation of the high abnormal activity followed by an increase in the number of the low frequency components toward the patients alpha-rhythm. The possible mechanisms of the effects of external magnetic stimulation on the pineal gland in the brain are presented. PMID:18431816

  19. Chaotic oscillations in electron beam with virtual cathode in external magnetic field

    NASA Astrophysics Data System (ADS)

    Hramov, A. E.; Koronovskiy, A. A.; Kurkin, S. A.; Rempen, I. S.

    2011-11-01

    This article presents the results of a numerical study of external magnetic field influence on the conditions and mechanisms of virtual cathode (VC) formation in a relativistic electron beam. It also considers other related issues, e.g. peculiarities of nonlinear dynamics of electron beam with VC under changed external magnetic field, different mechanisms of VC oscillation chaotisation leading to complication of vircator system dynamics and appearance of multi-frequency VC oscillations. General systemic mechanism of VC oscillation chaotisation has been identified which is connected with formation of electronic patterns in electron beam whose interaction in the common field of spatial charge determines appearance of additional inner feedback. Transition from chaotic to periodical oscillation regime is found to be connected with destroying the mechanism of secondary electronic structures (electron bunches) formation. Besides, the influence of extent of screening of electron gun from magnetic field is discussed.

  20. Manipulating Majorana zero modes on atomic rings with an external magnetic field

    NASA Astrophysics Data System (ADS)

    Li, Jian; Neupert, Titus; Bernevig, B. Andrei; Yazdani, Ali

    2016-01-01

    Non-Abelian quasiparticles have been predicted to exist in a variety of condensed matter systems. Their defining property is that an adiabatic braid between two of them results in a non-trivial change of the quantum state of the system. The simplest non-Abelian quasiparticles--the Majorana bound states--can occur in one-dimensional electronic nano-structures proximity-coupled to a bulk superconductor. Here we propose a set-up, based on chains of magnetic adatoms on the surface of a thin-film superconductor, in which the control over an externally applied magnetic field suffices to create and manipulate Majorana bound states. We consider specifically rings of adatoms and show that they allow for the creation, annihilation, adiabatic motion and braiding of pairs of Majorana bound states by varying the magnitude and orientation of the external magnetic field.

  1. Manipulating Majorana zero modes on atomic rings with an external magnetic field.

    PubMed

    Li, Jian; Neupert, Titus; Bernevig, B Andrei; Yazdani, Ali

    2016-01-01

    Non-Abelian quasiparticles have been predicted to exist in a variety of condensed matter systems. Their defining property is that an adiabatic braid between two of them results in a non-trivial change of the quantum state of the system. The simplest non-Abelian quasiparticles--the Majorana bound states--can occur in one-dimensional electronic nano-structures proximity-coupled to a bulk superconductor. Here we propose a set-up, based on chains of magnetic adatoms on the surface of a thin-film superconductor, in which the control over an externally applied magnetic field suffices to create and manipulate Majorana bound states. We consider specifically rings of adatoms and show that they allow for the creation, annihilation, adiabatic motion and braiding of pairs of Majorana bound states by varying the magnitude and orientation of the external magnetic field. PMID:26791080

  2. Manipulating Majorana zero modes on atomic rings with an external magnetic field

    PubMed Central

    Li, Jian; Neupert, Titus; Bernevig, B. Andrei; Yazdani, Ali

    2016-01-01

    Non-Abelian quasiparticles have been predicted to exist in a variety of condensed matter systems. Their defining property is that an adiabatic braid between two of them results in a non-trivial change of the quantum state of the system. The simplest non-Abelian quasiparticles—the Majorana bound states—can occur in one-dimensional electronic nano-structures proximity-coupled to a bulk superconductor. Here we propose a set-up, based on chains of magnetic adatoms on the surface of a thin-film superconductor, in which the control over an externally applied magnetic field suffices to create and manipulate Majorana bound states. We consider specifically rings of adatoms and show that they allow for the creation, annihilation, adiabatic motion and braiding of pairs of Majorana bound states by varying the magnitude and orientation of the external magnetic field. PMID:26791080

  3. On the interaction between the external magnetic field and nanofluid inside a vertical square duct

    SciTech Connect

    Ali, Kashif; Ahmad, Shabbir; Ahmad, Shahzad Ashraf, Muhammad; Asif, Muhammad

    2015-10-15

    In this paper, we numerically study how the external magnetic field influences the flow and thermal characteristics of nanofluid inside a vertical square duct. The flow is considered to be laminar and hydrodynamically as well as thermally developed, whereas the thermal boundary condition of constant heat flux per unit axial length with constant peripheral temperature at any cross section, is assumed. The governing equations are solved using the spectral method and the finite difference method. Excellent comparison is noted in the numerical results given by the two methods but the spectral method is found to be superior in terms of both efficiency and accuracy. We have noted that the flow reversal due to high Raleigh number may be controlled by applying an external magnetic field of suitable strength. Moreover, the Nusselt number is found to be almost a linear function of the nanoparticle volume fraction parameter, for different values of the Raleigh number and the magnetic parameter.

  4. Control of Magnetic States of Cobalt Nanorings by an External Azimuthal Field

    NASA Astrophysics Data System (ADS)

    Pradhan, Nihar; Yang, Tianyu; Licht, Abbey; Li, Yihan; Tuominen, Mark; Aidala, Katherine

    2011-03-01

    Ferromagnetic nanorings attract interest due to their potential application in high density data storage and Magnetoresistive Random Access Memory (MRAM) devices. These nanorings show multidomain stable states that need to be well controlled by external in-plane or circular magnetic fields. This talk presents a new method to generate circular magnetic fields to control the magnetic states in different geometries of Cobalt nanoring structures, of varying diameter, width and thickness. A solid platinum AFM tip was used to pass current through a single nanoring, generating a circular magnetic field. In applying this field we were able to change the state of the individual ring without affecting the states of other neighboring rings. The evolution of the magnetic states of individual symmetric and asymmetric Cobalt nanorings with applied azimuthal field will be presented. The work was supported by the National Science Foundation under DMR Grant 906832 and Research Corporation Grant 7889.

  5. Nonlinear Dynamics of Magnons observed by AC Spin Pumping in Magnetic Hybrid Structures

    NASA Astrophysics Data System (ADS)

    Vilela-Leao, L. H.; Cunha, R. O.; Azevedo, A.; Rodriguez-Suarez, R. L.; Rezende, S. M.

    2015-03-01

    The electron spin degree of freedom constitutes the basic means to carry and store information in the field of spintronics. In the spin pumping process, the microwave driven magnetization dynamics in a ferromagnetic film generates a spin current in an attached metallic layer that can be converted into a charge current by means of the inverse spin Hall effect and detected by a voltage signal. While the time independent component (DC) of the spin current has been widely investigated in a variety of material structures, recently it has been recognized that the alternating current (AC) component is much larger, though more difficult to detect, and has many attractive features. We report experiments with microwave driven DC and AC spin pumping in bilayers made of the insulating ferrimagnet yttrium iron garnet (YIG) and platinum that reveal the nonlinear dynamics involving the driven mode and a pair of magnon modes with half frequency. This process occurs when the frequency is lowered below a critical value so that a three-magnon splitting process with energy conservation is made possible. The results are explained by a model with coupled nonlinear equations describing the time evolution of the magnon modes.

  6. ac magnetic trackers for biomedical application: now and in the near future

    NASA Astrophysics Data System (ADS)

    Murry, Herschell F.

    1996-04-01

    A number of ac magnetic trackers have been, and are now being, used in the medical community for varied applications from describing electronically the exact shape of a subject to tracking movement of objects. A good reason for using this technology is that the magnetic fields pass through the body without occlusions and without ionizing radiation. This paper commences with descriptions of several such tools readily available, including our 3D input stylus and 3DRAW tablet defining object dimensions to 0.01' accuracy and our close-in Short Ranger transmitter operating precisely between 2' - 12' over the subject. For the future, R&D and military electronics sponsored topics such as a metal distortion insensitive magnetic source, a high performance 240 Hz (or up to eight sensors each operating at 30 Hz) tracker with the processing power to virtually eliminate metal distortion effects and an approach for building a biologically insertible tracker are discussed to indicate the potential for new tracking tools. Discussion of needs from the medical community is encouraged in order to better guide efforts in applying our specialty technology to biomedical applications where ewe are neophytes.

  7. Generation of liquid metal structures of high aspect ratio by application of an ac magnetic field

    NASA Astrophysics Data System (ADS)

    Andreev, Oleg; Pothérat, Alban; Thess, André

    2010-06-01

    We study how the shape of parts obtained through the LASER cladding process can be controlled by application of an ac magnetic field by means of two simple physical models: a numerical and an experimental one. More specifically, we show that straight metallic joints of high aspect ratio can be obtained by using inductors of triangular cross-section that concentrate electromagnetic forces at the bottom of the joint. The effect is first demonstrated on a numerical model for an infinitely long joint such as: we illustrate how the joint shape can be controlled by varying the inclination of the inductor and for a magnetic Bond number Bom=60 (which measures the ratio of electromagnetic to capillary forces), we obtain a joint of aspect ratio up to 7.2. We further find that inductor angles in the range 15°-25° lead to joint side faces that are close to vertical. These findings are then verified experimentally by placing a liquid metal drop in a purpose built inductor of triangular cross-section. We find a good agreement between the theoretical prediction of our two-dimensional model and the real three-dimensional drop. For the highest magnetic Bond number our generator could deliver, Bom=20.19, we achieved a drop aspect ratio of 2.73.

  8. Fluctuation-Induced Interactions in external magnetic fields: Casimir force and Radiative Heat Transfer

    NASA Astrophysics Data System (ADS)

    Esquivel-Sirvent, Raul

    Thermally induced electromagnetic fields give rise to the Casimir force and the near field heat transfer between two bodies separated by a gap. These phenomena are described by Rytova's theory of fluctuating electromagnetic fields and both the Casimir force and the near field heat transfer depend on the local dielectric function of the bodies. In this work we present a theoretical calculation on the modulation of fluctuation-induced interactions in the presence of an external magnetic field. The system consists of two parallel plates separated by a gap d. Each plate is isotropic and has a local dielectric function. Applying an external magnetic field parallel to the plates, in the so called Voigt configuration, the plates become anisotropic. In particular, we consider plates of InSb. For the Casimir force the two plates are kept at the same temperature and the external field reduces the magnitude of the force. Similarly if the two plates are kept at different temperature the near field radiative heat transfer is modulated by the magnitude of the external magnetic field. The results are extended to semiconducting quantum wells. In both cases, the excitation of magnetoplasmons provides an explanation for the observed effect.

  9. Modified MgFe2O4 Ferrimagnetic Nanoparticles to Improve Magnetic and AC Magnetically-Induced Heating Characteristics for Hyperthermia.

    PubMed

    Lee, Sanghoon; Jeun, Minhong

    2015-12-01

    A ferrimagnetic nanoparticle with a smaller size, a narrower size distribution, and a higher ac heat generation ability has been still studied for intra-arterial or intra-tumoral hyperthermia. In this study, we manipulate the calcining temperature in the range of 400-600 degrees C to modify MgFe2O4 ferrimagnetic nanoparticles (FMNPs) during modified sol-gel process. The modified MgFe2O4 FMNPs have well controlled with small size and narrow size distribution, so that their magnetic and ac magnetically-induced heating characteristics are significantly improved. In particular, MgFe2O4 nanoparticles synthesized at the calcining temperature of 600 degrees C and sintering temperature of 700 degrees C show the most suitable size (58 nm ± 13 nm) and its distribution (22%) resulting in the highest ac magnetically-induced heating temperature (T(AC,mag), ΔT = 93 degrees C) and SLP (Specific Loss Power, 600 W/g) at the biologically tolerable range of magnetic field (H(appl) = 140 Oe) and frequency (f(appl) = 110 kHz). It is found to be due to the improvement of magnetic softness and saturation magnetization resulting in the largest hysteresis loss power. All the results in this work clearly demonstrate that calcining process is one of the key parameters to control the proper size and size distribution for improving magnetic and ac magnetically-induced heating characteristics of MgFe2O4 FMNPs, which can be applicable to hyperthermia agents in nanomedicine. PMID:26682384

  10. Oscillatory magnetoconvective instability in a ferrofluid layer placed in an oblique external magnetic field

    NASA Astrophysics Data System (ADS)

    Suslov, Sergey A.; Rahman, Habibur; Bozhko, Aleksandra A.

    2014-11-01

    Magnetite-based ferrofluids are manufactured magneto-polarisable nanofluids that magnetize in an external magnetic field in a similar way to natural paramagnetic fluids(e.g. oxygen), however to a much higher degree. Paramagnetic and ferrofluid flows are described by similar equations and it is expected that they would exhibit a similar behaviour. Indeed we show that in both type of fluids the most prominent instability structures align with the in-layer field component and the onset of magnetoconvection is delayed by the field inclination. However we find that in contrast to paramagnetic fluids the instabilities arising in differentially heated ferrofluids placed in a uniform external oblique magnetic field are oscillatory. This is traced back to the nonlinearity of the magnetic field distribution induced inside the ferrofluid layer that arises whenever the direction of the applied magnetic field is not normal. Given that the magnetic field inclination with respect to the plane of the layer is inevitable near its edges the obtained stability results shed light on the possible reasons for the existnce of unsteady patterns that have been detected in the normal field experiments we reported previously.

  11. Use of an advanced composite material in construction of a high pressure cell for magnetic ac susceptibility measurements

    NASA Astrophysics Data System (ADS)

    Wang, X.; Misek, M.; Jacobsen, M. K.; Kamenev, K. V.

    2014-10-01

    The applicability of fibre-reinforced polymers for fabrication of high pressure cells was assessed using finite element analysis and experimental testing. Performance and failure modes for the key components of the cell working in tension and in compression were evaluated and the ways for optimising the designs were established. These models were used in construction of a miniature fully non-metallic diamond anvil cell for magnetic ac susceptibility measurements in a magnetic property measurement system. The cell is approximately 14 mm long, 8.5 mm in diameter and was demonstrated to reach a pressure of 5.6 GPa. AC susceptibility data collected on Dy2O3 demonstrate the performance of the cell in magnetic property measurements and confirm that there is no screening of the sample by the environment which typically accompanies the use of conventional metallic high pressure cells in oscillating magnetic fields.

  12. Edge pinch instability of liquid metal sheet in a transverse high-frequency ac magnetic field.

    PubMed

    Priede, Jānis; Etay, Jacqueline; Fautrelle, Yves

    2006-06-01

    We analyze the linear stability of the edge of a thin liquid metal layer subject to a transverse high-frequency ac magnetic field. The layer is treated as a perfectly conducting liquid sheet that allows us to solve the problem analytically for both a semi-infinite geometry with a straight edge and a thin disk of finite radius. It is shown that the long-wave perturbations of a straight edge are monotonically unstable when the wave number exceeds the critical value k(c) = F0/(gamma l0), which is determined by the linear density of the electromagnetic force F0 acting on the edge, the surface tension gamma, and the effective arclength of edge thickness l0. Perturbations with wavelength shorter than critical are stabilized by the surface tension, whereas the growth rate of long-wave perturbations reduces as similar to k for k --> 0. Thus, there is the fastest growing perturbation with the wave number k max = 2/3 k(c). When the layer is arranged vertically, long-wave perturbations are stabilized by the gravity, and the critical perturbation is characterized by the capillary wave number k(c) = square root of (g rho/gamma), where g is the acceleration due to gravity and rho is the density of metal. In this case, the critical linear density of electromagnetic force is F(0,c) = 2k(c)l0 gamma, which corresponds to the critical current amplitude I(0,c) = 4 square root of (pi k(c) l0L gamma/mu 0) when the magnetic field is generated by a straight wire at the distance L directly above the edge. By applying the general approach developed for the semi-infinite sheet, we find that a circular disk of radius R0 placed in a transverse uniform high-frequency ac magnetic field with the induction amplitude B0 becomes linearly unstable with respect to exponentially growing perturbation with the azimuthal wave number m = 2 when the magnetic Bond number exceeds Bm(c) = B(0)2 R(0)2 / (2 mu 0 l0 gamma) = 3 pi. For Bm > Bm(c), the wave number of the fastest growing perturbation is m(max) = [2

  13. Production Of Multi-magnetron Plasma By Using Polyphase Ac Glow Discharge In An Improved Multi-pole Magnetic Field

    NASA Astrophysics Data System (ADS)

    Matsumoto, Kazunori; Motoki, Kentaro; Miyamoto, Masahiro; Uetani, Yasuhiro

    1998-10-01

    Effects of an improved multi-pole magnetic field on a plasma production generated by a polyphase ac glow discharge with multiple electrodes have been investigated. Conventional configuration of the multi-pole magnetic filed has been modified to suppress plasma losses at both ends of the chamber due to ExB drift motion. The modified multi-pole magnetic field has enabled us to produce a multiple magnetron-plasma at a considerably low pressure less than mTorr. The low temperature plasma has been widely used as the fine processing technology of a dry etching and as the thin film formation technology of a sputtering coating. Large-scale plasmas which can be generated at a low gas-pressure have been desired for more wider dry etching and greater sputter coating. The purpose of this study is to develop a large-scale and low-cost plasma generator by using a polyphase ac power source with the low frequency. In this session, we will present the experimental result as to a multiple magnetron-plasma generated in the modified twenty-four poles magnetic field by using the twenty-four-phase ac power source with the commercial electric power frequency of 60Hz. The ac power is supplied to twenty-four electrodes which are fixed to the water-cooled chamber-wall through sheet insulators so that the electrodes can be cooled indirectly.

  14. Structural and Magnetic Study of Cu x FeCr1- x O2 Oxides Under High External Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Ozkendir, Osman Murat

    2013-06-01

    The structural, electronic, and magnetic behaviors of Cu x FeCr1- x O2 polycrystals are investigated. Investigations are conducted for increasing chromium substitution, according to varying x values in the formula versus copper, for x = 0, 0.2, 0.4, 0.6, 0.8, and 1. The magnetic response of polycrystalline samples under increasing external magnetic field from 0.4 T to 5 T is also studied. The partial crystal structure deformation/transition from delafossite CuFeO2 structure to corundum-type FeCrO3 structure containing CrO2 and Cr2O3 blocks is determined. The change in the crystal structure geometry with increasing Cr substitution is observed. Besides, prominent changes in magnetic ordering are observed from antiferromagnetic ( x = 1, 0.8, and 0.6) to ferromagnetic ordering ( x = 0.4 and 0.2) for high applied external magnetic fields above 2 T.

  15. Calibration of an inertial-magnetic measurement unit without external equipment, in the presence of dynamic magnetic disturbances

    NASA Astrophysics Data System (ADS)

    Metge, J.; Mégret, R.; Giremus, A.; Berthoumieu, Y.; Décamps, T.

    2014-12-01

    Inertial-magnetic measurement units are inexpensive sensors, widely used in electronic systems (smartphones, GPS, micro-UAV, etc). However the precision of these sensors is highly dependent on their calibration. This article proposes a complete solution to calibrate the sensors (accelerometers, gyrometers and magnetometers), the inter-sensor rotations and the dynamic disturbances of the magnetic field due to the immediate environment. Contrary to most of the existing techniques, the proposed method does not necessitate any external equipment, apart from the sensors already included in the system. The calibration can be performed by hand manipulation by the final user. Simulations and experiments show the advantages of the proposed approach.

  16. High sensitivity microwave detection using a magnetic tunnel junction in the absence of an external applied magnetic field

    SciTech Connect

    Gui, Y. S.; Bai, L. H.; Hu, C.-M.; Xiao, Y.; Guo, H.; Hemour, S.; Zhao, Y. P.; Wu, K.; Houssameddine, D.

    2015-04-13

    In the absence of any external applied magnetic field, we have found that a magnetic tunnel junction (MTJ) can produce a significant output direct voltage under microwave radiation at frequencies, which are far from the ferromagnetic resonance condition, and this voltage signal can be increase by at least an order of magnitude by applying a direct current bias. The enhancement of the microwave detection can be explained by the nonlinear resistance/conductance of the MTJs. Our estimation suggests that optimized MTJs should achieve sensitivities for non-resonant broadband microwave detection of about 5000 mV/mW.

  17. A study of the electromagnetic characteristics of no-insulation GdBCO racetrack coils under an external magnetic ripple field

    NASA Astrophysics Data System (ADS)

    Choi, Y. H.; Yang, D. G.; Kim, Y. G.; Kim, S. G.; Song, J. B.; Lee, H. G.

    2016-04-01

    Here we report the effect of an external magnetic ripple field on the electromagnetic characteristics of GdBCO racetrack coils being operated with a constant DC current. Two types of GdBCO racetrack coils, one wound without turn-to-turn insulation (NI) and the other wound with Kapton tape (INS), were examined under external ripple fields generated by a permanent magnet mounted on a rotor, which was driven by a separate AC motor. The voltage fluctuations and magnetic field variations were measured with respect to the external ripple field intensity (B ERF), rotating speed, and the operating condition. When the INS and NI coils were exposed to an external ripple field (herein, I op = 80 A, B ERF = 2 mT, and 5 rpm), a voltage fluctuation occurred because a time-varying magnetic field interacted with an electric circuit creating an electromotive force. The peak-to-peak voltage (V pp = 0.29 mV) of the NI coil was ∼1.86 times lower than that (0.54 mV) of the INS coil, because the voltage response of the NI coil lagged behind dB/dt due to the existence of turn-to-turn contact. Furthermore, the V pp of the INS coil increased with increasing B ERF and rotating speed, while those of the NI coil were barely affected due to the delay of electromagnetic induction. In excessive current and ripple field conditions (I op = 1.125 I c, B ERF = 8 mT, and 50 rpm) the INS coil eventually quenched while the NI coil did not, implying that the electromagnetic stability of the NI coil in excessive time-varying field conditions was superior to that of the INS coil.

  18. Effects of AC/DC magnetic fields, frequency, and nanoparticle aspect ratio on cellular transfection of gene vectors

    NASA Astrophysics Data System (ADS)

    Ford, Kris; Mair, Lamar; Fisher, Mike; Rowshon Alam, Md.; Juliano, Rudolph; Superfine, Richard

    2008-10-01

    In order to make non-viral gene delivery a useful tool in the study and treatment of genetic disorders, it is imperative that these methodologies be further refined to yield optimal results. Transfection of magnetic nanoparticles and nanorods are used as non-viral gene vectors to transfect HeLa EGFP-654 cells that stably express a mutated enhanced green fluorescent protein (EGFP) gene. We deliver antisense oligonucleotides to these cells designed to correct the aberrant splicing caused by the mutation in the EGFP gene. We also transfect human bronchial endothelial cells and immortalized WI-38 lung cells with pEGFP-N1 vectors. To achieve this we bind the genes to magnetic nanoparticles and nanorods and introduce magnetic fields to effect transfection. We wish to examine the effects of magnetic fields on the transfection of these particles and the benefits of using alternating (AC) magnetic fields in improving transfection rates over direct (DC) magnetic fields. We specifically look at the frequency dependence of the AC field and particle aspect ratio as it pertains to influencing transfection rate. We posit that the increase in angular momentum brought about by the AC field and the high aspect ratio of the nanorod particles, is vital to generating the force needed to move the particle through the cell membrane.

  19. Critical field measurements in superconductors using ac inductive techniques

    NASA Astrophysics Data System (ADS)

    Campbell, S. A.; Ketterson, J. B.; Crabtree, G. W.

    1983-09-01

    The ac in-phase and out-of-phase response of type II superconductors is discussed in terms of dc magnetization curves. Hysteresis in the dc magnetization is shown to lead to a dependence of the ac response on the rate at which an external field is swept. This effect allows both Hc1 and Hc2 to be measured by ac techniques. A relatively simple mutual inductance bridge for making such measurements is described in the text, and factors affecting bridge sensitivity are discussed in the Appendix. Data for the magnetic superconductor ErRh4B4 obtained using this bridge are reported.

  20. Solitonic modulation and Lifshitz point in an external magnetic field within Nambu-Jona-Lasinio model

    NASA Astrophysics Data System (ADS)

    Cao, Gaoqing; Huang, Anping

    2016-04-01

    We study the inhomogeneous solitonic modulation of a chiral condensate within the effective Nambu-Jona-Lasinio model when a constant external magnetic field is present. The self-consistent Pauli-Villars regularization scheme is adopted to manipulate the ultraviolet divergence encountered in the thermodynamic quantities. In order to efficiently determine the chiral restoration lines, a new kind of Ginzburg-Landau expansion approach is proposed here. At zero temperature, we find that both the upper and lower boundaries of the solitonic modulation oscillate with the magnetic field in the μ - B phase diagram which is actually the de Hass-van Alphan (dHvA) oscillation. It is very interesting to find out how the tricritical Lifshitz point (TL,μL) evolves with the magnetic field: There are also dHvA oscillations in the TL- B and μL- B curves, though the tricritical temperature TL increases monotonically with the magnetic field.

  1. External magnetic field influence on properties of high-power laser-produced plasma

    NASA Astrophysics Data System (ADS)

    Wołowski, J.; Kasperczuk, A.; Pisarczyk, T.

    1996-03-01

    The paper presents results of formation of expanding plasma by combining laser-produced plasma with an external strong magnetic field. The plasma was generated by means of a Nd-glass laser which was focused on a solid target located on the axis of a single-turn coil providing magnetic field of up to 50 T. Spatial characteristics of the dynamics of interaction of the plasma with the magnetic field were registered by means of a three-frame interferometry. For registration and analysis of interferograms, CCD cameras and a multichannel image acquisition system were used. An interesting influence of the strong magnetic field on the plasma dynamics and shape was observed. Preliminary results of numerical modelling are compared with the experimental data.

  2. Second VAMAS a.c. loss measurement intercomparison: a.c. magnetization measurement of hysteresis and coupling losses in NbTi multifilamentary strands

    NASA Astrophysics Data System (ADS)

    Schmidt, C.; Itoh, K.; Wada, H.

    The article summarizes results of part of the second VAMAS a.c. loss measurement intercomparison. This program was carried out at 17 participating laboratories on two sets of multifilamentary NbTi strands (Set No. 1: copper matrix, fil. diam. between 0.5 and 12 μm; Set No. 2: cupronickel matrix, fil. diam. between 0.4 and 1.2 μm). The results reported here were measured by means of a.c. magnetization methods and separated into hysteresis and coupling losses. One laboratory used a calorimetric method. The data scatter in measured hysteresis losses among the participating laboratories was reasonably small for different measuring methods adopted and experimental arrangements used. On the other hand, the data scatter in coupling losses was large, mainly because in most laboratories a.c. losses were measured only at low frequencies (below 1 Hz), where the separation of coupling losses from total losses tends to be inaccurate. The comparison of measured hysteresis losses with the critical state model showed a large disagreement, which is assumed to be due to proximity effect coupling between filaments. 1997 Elsevier Science Limited

  3. Dynamic and physical properties of ferrosuspensions with a structure rearranged by an external magnetic field

    SciTech Connect

    Shul'man, Z.P.; Demchuk, S.A.; Khusid, B.M.; Kordonskii, V.I.; Prokhorov, I.V.; Zal'tsgendler, A.E.

    1985-04-01

    This paper discusses micromechanics and structure of magnetorheological suspensions. Experimental investigation gives grounds for using the statistical theory of the flow of dilute suspensions of magnetic ellipsoidal particles in an external magnetic field. The basic principles of theory are described. It is observed in the experiments that the effective viscosity of such suspensions is high in comparison with that of the supporting medium; this is due to the dissipation of energy when the liquid flows past the solid phase. On the whole, the authors feel that the agreement of all the experimental and calculated data should be considered satisfactory.

  4. Structurization of ferrofluids in the absence of an external magnetic field

    SciTech Connect

    Zubarev, A. Yu. Iskakova, L. Yu.

    2013-02-15

    Structural transformations in a model ferrofluid in the absence of an external magnetic field have been theoretically studied. The results agree with well-known laboratory experiments and computer simulations in showing that, if the concentration of particles and their magnetic interaction energy are below certain critical values, most particles form separate linear chains. If these parameters exceed the critical values, most particles concentrate so as to form branched network structures. The passage from chains to network has a continuous character rather than represents a discontinuous first-order phase transition.

  5. Phase transition and critical end point driven by an external magnetic field in asymmetric quark matter

    NASA Astrophysics Data System (ADS)

    Costa, Pedro; Ferreira, Márcio; Hansen, Hubert; Menezes, Débora P.; Providência, Constança

    2014-03-01

    The location of the critical end point (CEP) in the QCD phase diagram is determined under different scenarios. The effect of strangeness, isospin/charge asymmetry and an external magnetic field is investigated. The discussion is performed within the 2+1 flavor Nambu-Jona-Lasinio model with Polyakov loop. It is shown that isospin asymmetry shifts the CEP to larger baryonic chemical potentials and smaller temperatures. At large asymmetries the CEP disappears. However, a strong enough magnetic field drives the system into a first order phase transition.

  6. The magnetisation profiles and ac magnetisation losses in a single layer YBCO thin film caused by travelling magnetic field waves

    NASA Astrophysics Data System (ADS)

    Wang, Wei; Coombs, Timothy

    2015-05-01

    This paper studies the magnetisation and ac magnetisation losses caused by a travelling magnetic wave on a single-layer YBCO thin film. This work provides thorough investigations on how the critical magnetic field gradient has been changed by the application of a travelling wave. Several conditions were studied such as zero-field cooling (ZFC), field cooling (FC) and a delta-shaped trapped field. It was found that the travelling wave tends to attenuate the existing critical magnetic field gradients in all these conditions. This interesting magnetic behaviour can be well predicted by the finite element (FEM) software with the E-J power law and Maxwell’s equations. The numerical simulations show that the existing critical current density has been compromised after applying the travelling wave. The magnetisation profile caused by the travelling wave is very different from the standing wave, while the magnetisation based on the standing wave can be interpreted by the Bean model and constant current density assumption. Based on the numerical method, which has reliability that has been solidly proven in the study, we have extended the study to the ac magnetisation losses. Comparisons were made between the travelling wave and the standing wave for this specific YBCO sample. It was found that by applying the magnetic wave of the same amplitude, the ac magnetisation loss caused by the travelling wave is about 1/3 of that caused by the standing wave. These results are helpful in understanding the general magnetism problems and ac magnetisation loss in the travelling magnetic wave conditions such as inside a high temperature superconducting (HTS) rotating machine, etc.

  7. Self-assembly mechanism of Ni nanowires prepared with an external magnetic field.

    PubMed

    Li, Xiaoyu; Wang, Hu; Xie, Kenan; Long, Qin; Lai, Xuefei; Liao, Li

    2015-01-01

    Nickel nanowires with a mean diameter of about 95 nm and lengths of up to 26 μm were prepared by a chemical reduction method in aqueous solution under an external magnetic field. The self-assembly mechanism was investigated in detail. The results indicate that the self-assembly process of Ni nanowires consists of three stages: nucleation and growth, ordered alignment and self-assembly, and deposition on the surface and gaps between the nickel particles. The self-assembly phenomenon occurs only when nickel particles grow to a size of about 60 nm in the reaction system. This critical size, which is proposed for the first time, is very important to comprehend the self-assembly mechanism of Ni nanowires prepared with an external magnetic field. PMID:26665084

  8. Electromagnetically induced transparency in a spherical quantum dot with hydrogenic impurity in the external magnetic field

    NASA Astrophysics Data System (ADS)

    Pavlović, Vladan; Stevanović, Ljiljana

    2016-04-01

    In this paper we analyzed the realization of the electromagnetically induced transparency (EIT) effect in the spherical quantum dot with on-center hydrogenic impurity under the influence of the external magnetic field. Three energy levels of hydrogen impurity 1s0, 2p-1, and 3d-2, together with the probe and control laser fields, which induce σ- transitions between the given states, form a ladder configuration. Optical Bloch equations for such a system are solved in a stationary regime. Dependence of the susceptibility for such a system on the Rabi frequency of the control field, intensity of the external magnetic field, detuning of the control field, and decay rates coefficients are then discussed in detail. Finally, the explanation in dressed state picture is given.

  9. On Cluster Properties of Classical Ferromagnets in an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Fröhlich, Jürg; Rodríguez, Pierre-François

    2016-06-01

    Correlation functions of ferromagnetic spin systems satisfying a Lee-Yang property are studied. It is shown that, for classical systems in a non-vanishing uniform external magnetic field h, the connected correlation functions decay exponentially in the distances between the spins, i.e., the inverse correlation length ("mass gap"), m(h), is strictly positive. Our proof is very short and transparent and is valid for complex values of the external magnetic field h, provided that Re h not = 0 . It implies a mean-field lower bound on m(h), as h searrow 0 , first established by Lebowitz and Penrose for the Ising model. Our arguments also apply to some quantum spin systems.

  10. Use of external magnetic fields in hohlraum plasmas to improve laser-coupling

    SciTech Connect

    Montgomery, D. S. Albright, B. J.; Kline, J. L.; Yin, L.; Barnak, D. H.; Chang, P. Y.; Davies, J. R.; Fiksel, G.; Froula, D. H.; Betti, R.; MacDonald, M. J.; Sefkow, A. B.

    2015-01-15

    Efficient coupling of laser energy into hohlraum targets is important for indirect drive ignition. Laser-plasma instabilities can reduce coupling, reduce symmetry, and cause preheat. We consider the effects of an external magnetic field on laser-energy coupling in hohlraum targets. Experiments were performed at the Omega Laser Facility using low-Z gas-filled hohlraum targets which were placed in a magnetic coil with B{sub z} ≤ 7.5-T. We found that an external field B{sub z} = 7.5-T aligned along the hohlraum axis results in up to a 50% increase in plasma temperature as measured by Thomson scattering. The experiments were modeled using the 2-D magnetohydrodynamics package in HYDRA and were found to be in good agreement.

  11. Use of external magnetic fields in hohlraum plasmas to improve laser-coupling

    NASA Astrophysics Data System (ADS)

    Montgomery, D. S.; Albright, B. J.; Barnak, D. H.; Chang, P. Y.; Davies, J. R.; Fiksel, G.; Froula, D. H.; Kline, J. L.; MacDonald, M. J.; Sefkow, A. B.; Yin, L.; Betti, R.

    2015-01-01

    Efficient coupling of laser energy into hohlraum targets is important for indirect drive ignition. Laser-plasma instabilities can reduce coupling, reduce symmetry, and cause preheat. We consider the effects of an external magnetic field on laser-energy coupling in hohlraum targets. Experiments were performed at the Omega Laser Facility using low-Z gas-filled hohlraum targets which were placed in a magnetic coil with Bz ≤ 7.5-T. We found that an external field Bz = 7.5-T aligned along the hohlraum axis results in up to a 50% increase in plasma temperature as measured by Thomson scattering. The experiments were modeled using the 2-D magnetohydrodynamics package in HYDRA and were found to be in good agreement.

  12. Use of external magnetic fields in hohlraum plasmas to improve laser-coupling

    DOE PAGESBeta

    Montgomery, D. S.; Albright, B. J.; Barnak, D. H.; Chang, P. Y.; Davies, J. R.; Fiksel, G.; Froula, D. H.; Kline, J. L.; MacDonald, M. J.; Sefkow, A. B.; et al

    2015-01-13

    Efficient coupling of laser energy into hohlraum targets is important for indirect drive ignition. Laser-plasma instabilities can reduce coupling, reduce symmetry, and cause preheat. We consider the effects of an external magnetic field on laser-energy coupling in hohlraum targets. Experiments were performed at the Omega Laser Facility using low-Z gas-filled hohlraum targets which were placed in a magnetic coil with Bz ≤ 7.5-T. We found that an external field Bz = 7.5-T aligned along the hohlraum axis results in up to a 50% increase in plasma temperature as measured by Thomson scattering. As a result, the experiments were modeled usingmore » the 2-D magnetohydrodynamics package in HYDRA and were found to be in good agreement.« less

  13. Use of external magnetic fields in hohlraum plasmas to improve laser-coupling

    SciTech Connect

    Montgomery, D. S.; Albright, B. J.; Barnak, D. H.; Chang, P. Y.; Davies, J. R.; Fiksel, G.; Froula, D. H.; Kline, J. L.; MacDonald, M. J.; Sefkow, A. B.; Yin, L.; Betti, R.

    2015-01-13

    Efficient coupling of laser energy into hohlraum targets is important for indirect drive ignition. Laser-plasma instabilities can reduce coupling, reduce symmetry, and cause preheat. We consider the effects of an external magnetic field on laser-energy coupling in hohlraum targets. Experiments were performed at the Omega Laser Facility using low-Z gas-filled hohlraum targets which were placed in a magnetic coil with Bz ≤ 7.5-T. We found that an external field Bz = 7.5-T aligned along the hohlraum axis results in up to a 50% increase in plasma temperature as measured by Thomson scattering. As a result, the experiments were modeled using the 2-D magnetohydrodynamics package in HYDRA and were found to be in good agreement.

  14. Self-assembly mechanism of Ni nanowires prepared with an external magnetic field

    PubMed Central

    Li, Xiaoyu; Wang, Hu; Xie, Kenan; Long, Qin; Lai, Xuefei

    2015-01-01

    Summary Nickel nanowires with a mean diameter of about 95 nm and lengths of up to 26 μm were prepared by a chemical reduction method in aqueous solution under an external magnetic field. The self-assembly mechanism was investigated in detail. The results indicate that the self-assembly process of Ni nanowires consists of three stages: nucleation and growth, ordered alignment and self-assembly, and deposition on the surface and gaps between the nickel particles. The self-assembly phenomenon occurs only when nickel particles grow to a size of about 60 nm in the reaction system. This critical size, which is proposed for the first time, is very important to comprehend the self-assembly mechanism of Ni nanowires prepared with an external magnetic field. PMID:26665084

  15. Sensor-less pseudo-sinusoidal drive for a permanent-magnet brushless ac motor

    NASA Astrophysics Data System (ADS)

    Liu, Li-Hsiang; Chern, Tzuen-Lih; Pan, Ping-Lung; Huang, Tsung-Mou; Tsay, Der-Min; Kuang, Jao-Hwa

    2012-04-01

    The precise rotor-position information is required for a permanent-magnet brushless ac motor (BLACM) drive. In the conventional sinusoidal drive method, either an encoder or a resolver is usually employed. For position sensor-less vector control schemes, the rotor flux estimation and torque components are obtained by complicated coordinate transformations. These computational intensive methods are susceptible to current distortions and parameter variations. To simplify the method complexity, this work presents a sensor-less pseudo-sinusoidal drive scheme with speed control for a three-phase BLACM. Based on the sinusoidal drive scheme, a floating period of each phase current is inserted for back electromotive force detection. The zero-crossing point is determined directly by the proposed scheme, and the rotor magnetic position and rotor speed can be estimated simultaneously. Several experiments for various active angle periods are undertaken. Furthermore, a current feedback control is included to minimize and compensate the torque fluctuation. The experimental results show that the proposed method has a competitive performance compared with the conventional drive manners for BLACM. The proposed scheme is straightforward, bringing the benefits of sensor-less drive and negating the need for coordinate transformations in the operating process.

  16. The attenuation of the levitation force of HTS bulk exposed to AC magnetic field on the above NdFeB guideway

    NASA Astrophysics Data System (ADS)

    Liu, Minxian; Wang, Yan

    2012-01-01

    In the present High Temperature Superconducting (HTS) maglev vehicle system, the air gaps between the adjacent permanent magnets make the magnetic fields above the NdFeB guideway non-uniform. So it is required to study the characteristics of levitation force of the HTS bulk affected by the non-uniform applied magnetic fields along the moving direction. In this paper, we have studied the characteristics of the levitation force relaxation by an experiment in which AC magnetic field generated by an electromagnet is used to simulate the time-varying magnetic field caused by the inhomogeneity of the NdFeB guideway. From the experiment results, it is found that the levitation force is attenuated with the application of the AC field, and the attenuation is increased with the amplitude of the AC field, but the attenuation is almost independent of the frequency the AC magnetic field.

  17. Analysis and comparison for rotor eddy current losses of permanent magnet synchronous generator according to dc and ac load conditions

    NASA Astrophysics Data System (ADS)

    Jang, Seok-Myeong; Kim, Hyun-Kyu; Choi, Jang-Young; Ko, Kyoung-Jin

    2009-04-01

    This paper presents an analytical procedure for the calculation of the eddy current losses of permanent magnet synchronous generator (PMSG). The dc and ac loading effects on the eddy current is examined through the suggested analytical procedure that considers the radial and tangential flux density waveform through a phase current harmonic analysis. The corresponding test results are also presented to quantify and compare those loading effects on the eddy current. The results verified the suggested analytical procedures and show that the rotor eddy current losses for PMSG with the dc loads turned out to be more significant than those with the ac loads.

  18. Analyze and experiment on AC magnetic field's effect to fiber optic gyroscopes in compact stabilization control systems

    NASA Astrophysics Data System (ADS)

    Zhang, Chao; Mao, Yao; Tian, Jing; Li, Zhijun

    2015-10-01

    Fiber optic gyroscopes (FOG) are getting more and more attention in areas such as stabilization control systems as they are all solid state and have a wide bandwidth. In stabilization systems that require wide bandwidth control, motors are usually used as actuating mechanism for active disturbance restrain. Voice coil motors (VCMs) are usually used in compact stabilization systems that require large torque and fast response. However, AC magnetic field, which can affect the output of FOG due to Faraday effect, will be generated during operation of VCMs. The frequency range affected by the AC magnetic field to the FOG's output is the same as VCMs drive signal frequency range, which is also exactly the stabilization system's working range. Therefore the effect of the AC magnetic field to FOGs must be evaluated to verify the feasibility of a stable system design that uses both FOGs and VCMs. In this article, the basic structure and operating principle of stabilization system is introduced. The influence of AC magnetic field to FOG is theoretically analyzed. The magnetic field generated by VCMs is numerically simulated based on the theory deduction of the magnetic field near energized wires. To verify the influence of the VCM generated magnetic field to the FOGs in practical designs, a simplified random fiber coil model is built for it's hard to accurately test the exact polarize axis's twisting rate in a fiber coil. The influence to the FOG's output of different random coil model is simulated and the result shows a same trend that the influence of the VCM's magnetic field to the FOG is reduced as the distance between the VCM and the FOG increasing. The influence of a VCM to a FOG with the same parameters is experimentally tested. In the Fourier transformed FOG data the same frequency point as the VCM drive signal frequency can be read. The result fit simulated result that as the distance increases, the influence decreases. The amplitude of the frequency point is just

  19. Synthesis of cobalt nanowires in aqueous solution under an external magnetic field

    PubMed Central

    Li, Xiaoyu; Sun, Lijuan; Wang, Hu; Xie, Kenan; Long, Qin; Lai, Xuefei

    2016-01-01

    Summary In contrast to the majority of related experiments, which are carried out in organic solvents at high temperatures and pressures, cobalt nanowires were synthesized by chemical reduction in aqueous solution with the assistance of polyvinylpyrrolidone (PVP) as surfactant under moderate conditions for the first time, while an external magnetic field of 40 mT was applied. Uniform linear cobalt nanowires with relatively smooth surfaces and firm structure were obtained and possessed an average diameter of about 100 nm with a coating layer of PVP. By comparison, the external magnetic field and PVP were proven to have a crucial influence on the morphology and the size of the synthesized cobalt nanowires. The prepared cobalt nanowires are crystalline and mainly consist of cobalt as well as a small amount of platinum. Magnetic measurements showed that the resultant cobalt nanowires were ferromagnetic at room temperature. The saturation magnetization (M s) and the coercivity (H c) were 112.00 emu/g and 352.87 Oe, respectively. PMID:27547616

  20. Synthesis of cobalt nanowires in aqueous solution under an external magnetic field.

    PubMed

    Li, Xiaoyu; Sun, Lijuan; Wang, Hu; Xie, Kenan; Long, Qin; Lai, Xuefei; Liao, Li

    2016-01-01

    In contrast to the majority of related experiments, which are carried out in organic solvents at high temperatures and pressures, cobalt nanowires were synthesized by chemical reduction in aqueous solution with the assistance of polyvinylpyrrolidone (PVP) as surfactant under moderate conditions for the first time, while an external magnetic field of 40 mT was applied. Uniform linear cobalt nanowires with relatively smooth surfaces and firm structure were obtained and possessed an average diameter of about 100 nm with a coating layer of PVP. By comparison, the external magnetic field and PVP were proven to have a crucial influence on the morphology and the size of the synthesized cobalt nanowires. The prepared cobalt nanowires are crystalline and mainly consist of cobalt as well as a small amount of platinum. Magnetic measurements showed that the resultant cobalt nanowires were ferromagnetic at room temperature. The saturation magnetization (M s) and the coercivity (H c) were 112.00 emu/g and 352.87 Oe, respectively. PMID:27547616

  1. Control of lunar external magnetic enhancements by IMF polarity: A case study

    NASA Astrophysics Data System (ADS)

    Nishino, Masaki N.; Fujimoto, Masaki; Tsunakawa, Hideo; Matsushima, Masaki; Shibuya, Hidetoshi; Shimizu, Hisayoshi; Takahashi, Futoshi; Saito, Yoshifumi; Yokota, Shoichiro

    2012-12-01

    We study an interaction between the solar wind and crustal magnetic fields on the lunar surface using SELENE (Kaguya) data. It has been known that magnetic enhancements are at times detected near the limb external to the lunar wake, which is thus called lunar external magnetic enhancement (LEME), as a result of direct interaction between the solar wind and lunar crustal fields. Although previous observational studies showed that LEMEs in the high solar zenith angle region favor stronger interplanetary magnetic field (IMF) and higher solar wind density, the relation between the IMF and the crustal field orientation has not been taken into account. We show evidence that the relation between the IMF and crustal field orientation is also one of the key factors that control the extent of LEME, focusing on one-day observations at 100 km altitude that include data above strong crustal fields around South Pole-Aitken (SPA) basin. Strong LEMEs are detected at 100 km altitude around SPA basin under the stronger and northward IMF condition, while they weaken under southward IMF. All LEME's peaks are located in the region where unperturbed crustal fields at 300 km altitude are directed northward while they are less related to unperturbed crustal fields at 100 km or lower, which suggests that lunar crustal fields are compressed by the solar wind dynamic pressure, and its large scale component parallel to the IMF is essential to the formation of the LEME.

  2. Nuclear-spin-induced cotton-mouton effect in a strong external magnetic field.

    PubMed

    Fu, Li-Juan; Vaara, Juha

    2014-08-01

    Novel, high-sensitivity and high-resolution spectroscopic methods can provide site-specific nuclear information by exploiting nuclear magneto-optic properties. We present a first-principles electronic structure formulation of the recently proposed nuclear-spin-induced Cotton-Mouton effect in a strong external magnetic field (NSCM-B). In NSCM-B, ellipticity is induced in a linearly polarized light beam, which can be attributed to both the dependence of the symmetric dynamic polarizability on the external magnetic field and the nuclear magnetic moment, as well as the temperature-dependent partial alignment of the molecules due to the magnetic fields. Quantum-chemical calculations of NSCM-B were conducted for a series of molecular liquids. The overall order of magnitude of the induced ellipticities is predicted to be 10(-11) -10(-6) rad T(-1)  M(-1)  cm(-1) for fully spin-polarized nuclei. In particular, liquid-state heavy-atom systems should be promising for experiments in the Voigt setup. PMID:24862946

  3. Epithelial internalization of superparamagnetic nanoparticles and response to external magnetic field.

    PubMed

    Dormer, Kenneth; Seeney, Charles; Lewelling, Kevin; Lian, Guoda; Gibson, Donald; Johnson, Matthew

    2005-05-01

    Superparamagnetic magnetite nanoparticles (MNP) coated with silica were synthesized and chronically implanted into the middle ear epithelial tissues of a guinea pig model (n=16) for the generation of force by an external magnetic field. In vivo limitations of biocompatibility include particle morphology, size distribution, composition and mode of internalization. Synthesis of MNP was performed using a modified precipitation technique and they were characterized by transmission electron microscopy, X-ray diffractometry and energy dispersive spectroscopy, which verified size distribution, composition and silica encapsulation. The mechanism for internalizing 16+/-2.3 nm diameter MNP was likely endocytosis, enhanced by magnetically force. Using sterile technique, middle ear epithelia of tympanic membrane or ossicles was exposed and a suspension of particles with fluoroscein isothiocyanate (FITC) label applied to the surface. A rare earth, NdFeBo magnet (0.35 T) placed under the animal, was used to pull the MNP into the tissue. After 8 days, following euthanasia, tissues were harvested and confocal scanning laser interferometry was used to verify intracellular MNP. Displacements of the osscicular chain in response to an external sinusoidal electromagnetic field were also measured using laser Doppler interferometry. We showed for the first time a physiologically relevant, biomechanical function, produced by MNP responding to a magnetic field. PMID:15576180

  4. Interior Vector Magnetic Field Monitoring via External Measurements for the SNS Neutron EDM Experiment

    NASA Astrophysics Data System (ADS)

    Nouri, Nima; Brown, Michael; Carr, Robert; Filippone, Bradley; Osthelder, Charles; Plaster, Bradley; Slutsky, Simon; Swank, Christopher

    2015-10-01

    A prototype of a magnetic field monitoring system designed to reconstruct the vector magnetic field components (and, hence, all nine of the ∂Bi / ∂xj field gradients) within the interior measurement fiducial volume solely from external measurements is under development for the SNS neutron EDM experiment. A first-generation room-temperature prototype array has already been tested. A second-generation prototype array consisting of 12 cryogenic-compatible fluxgate magnetometer probes will be deployed within the cold region of the experiment's 1 / 3 -scale cryogenic magnet testing apparatus. We will report progress towards the development of this second-generation prototype. This work was supported in part by the U. S. Department of Energy Office of Nuclear Physics under Award No. DE-FG02-08ER41557.

  5. Precision Hyperfine Structure of 2;^3P State of ^3He with External Magnetic

    NASA Astrophysics Data System (ADS)

    Wu, Qixue; Drake, G. W. F.

    2007-06-01

    The theory of the Zeeman effect can be used to extrapolate precise measurements for the fine structure or the hyperfine structure to zero-field strength. In the present work, the hyperfine structure of 2;^3P state of ^3He with external magnetic fields is precisely calculated. The values of the fields for 32 crossings and five anticrossings of the magnetic sublevels are theoretically predicted for magnetic field strengths up to 1 Tesla. The results are compared with experimental work. We include the linear terms, diamagnetic terms, and the 2̂ relativistic correction terms in the Zeeman Hamiltonian. All related matrix elements are calculated with high accuracy by the use of double basis set Hylleraas type variational wave functions[1,2].[1] Z. -C. Yan and G.W.F. Drake, Phys. Rev. A 50, R1980 (1994).[2] Q. Wu and G.W.F. Drake, J. Phys. B 40, 393 (2007).

  6. Study of the Dependence on Magnetic Field and Bias Voltage of an AC-Biased TES Microcalorimeter

    NASA Technical Reports Server (NTRS)

    Bandler, Simon

    2011-01-01

    At SRON we are studying the performance of a Goddard Space Flight Center single pixel TES microcalorimeter operated in the AC bias configuration. For x-ray photons at 6keV the AC biased pixel shows a best energy resolution of 3.7eV, which is about a factor of 2 worse than the energy resolution observed in identical DC-biased pixels. To better understand the reasons of this discrepancy, we investigated the detector performance as a function of temperature, bias working point and applied magnetic field. A strong periodic dependence of the detector noise on the TES AC bias voltage is measured. We discuss the results in the framework of the recent weak-link behaviour observed inTES microcalorimeters.

  7. Effect of External Magnetic Fields on the Operation of RF Cavities

    SciTech Connect

    Stratakis, D.; Berg, J.; Gallardo, J.C.; Palmer, R. B.

    2010-12-01

    Recent experiments have shown severe surface damage and a reduction of the maximum accelerating gradient for an rf cavity that is operating under external magnetic fields. This implies that serious problems may occur in lattices where rf cavities and external magnetic fields coexist, such as those of the proposed neutrino factory and muon collider. Although existing data suggest that this magnetic field dependent breakdown is associated with the emission of electrons from locally enhanced field regions on the cavity surface, the mechanism that drives this effect is not yet well understood. Here, we show that such field emitted electrons are accelerated by the cavity and focused by the magnetic field to the other side of the cavity where they heat its surface. We show that if the magnetic field is strong, significant surface deformation can occur that eventually could limit the accelerating gradient of the cavity. Results of our model are compared to the existing experimental data from an 805 MHz cavity. The geometry of the pillbox cavity in our case is more complicated, and the analysis depends on the electron energies, focused dimensions, and angle of impact, but damage may reasonably be expected with similar cyclical heating above 40 C. However, it is not yet known what the mechanism is for such surface damage to cause a cavity to breakdown. One possibility is that if electrons are focused on a location with a high surface gradient, then the local damage will generate new asperities with higher FN enhancement factors, thus initiating breakdown. While our preliminary analysis offers some quantification on the effects of the magnetic fields on the cavity's operation, other theoretical issues were not addressed. For instance, emission from secondary electrons was disregarded, the asperity was placed on axis, the magnetic field was assumed as uniform, the thermal-diffusion calculation ignored the shape of the rise time, and adopted an approximate calculation. On the

  8. Nuclear magnetic resonance of external protons using continuous dynamical decoupling with shallow NV centers

    NASA Astrophysics Data System (ADS)

    de Las Casas, Charles; Ohno, Kenichi; Awschalom, David D.

    2015-03-01

    The nitrogen vacancy (NV) center in diamond is a paramagnetic defect with excellent spin properties that can reside within a few nanometers of the diamond surface, enabling atomic-scale magnetic resonance sensing of external nuclear spins. Here we use rotating frame longitudinal spin relaxation (T1ρ) based sensing schemes, known as Continuous Dynamical Decoupling (CDD), to detect external nuclear spins with shallow NV centers (<5 nm from the surface). Distinguishing neighboring nuclear spins from each other requires the NV center be near enough to create differences in the hyperfine shifts and coupling strengths of the nuclei. However, spin coherence time and consequently the sensitivity of dynamical decoupling techniques degrade sharply as NVs become shallower. We use strong continuous driving to overcome this fast decoherence and detect an ensemble of external nuclear spins using a single shallow NV center with a short T2 (<2 μs) at magnetic fields as high as 0.5 Tesla. The increased sensitivity of this method relative to pulsed dynamical decoupling techniques demonstrates the benefits of CDD for sensing with very shallow NV centers. This work was supported by DARPA, AFOSR, and the DIAMANT program.

  9. Size-Dependent Multi- to Single Domain Transition of UV Laser-Driven Ferromagnetic Co Nanoparticles Under External Magnetic Field.

    PubMed

    Lee, Jun Seok; Lee, Ja Bin; Yang, Jung Yup; Hong, Jin Pyo

    2015-06-01

    The magnetic domain of cobalt (Co) nanoparticles (NPs) was studied as a function of particle size. Various single crystalline and uniform Co NPs were prepared using a novel UV laser irradiation technique on ultra thin Co films under an external applied magnetic field. Structural and magnetic characteristics were analyzed with transmission electron microscopy and superconducting quantum interference devices. The experimental observations indicate that during Co NP growth, externally applied magnetic fields and size-dependent NP surface effects strongly facilitate multi-to-single domain transition at a critical diameter of about 10 nm, an extremely small NP size that is suitable for higher density storage applications. PMID:26369084

  10. AC magnetic response of superconducting YBa2Cu3O7/PrBa2Cu3O7 superlattices

    NASA Astrophysics Data System (ADS)

    Miu, L.; Ivan, I.; Ionescu, A. M.; Miu, D.

    2016-06-01

    Vortex activation energy UAC in the critical-state related AC magnetic response of superconductors (appearing in the vicinity of the DC irreversibility line) takes large values, as often reported, which is not yet understood. This behavior is essentially different from that of the vortex-creep activation energy at long relaxation time scales, and may become important for AC applications of superconductors. To elucidate this aspect, we investigated the AC signal of almost decoupled [Y Ba2Cu3O7]n/[PrBa2Cu3O7]4 superlattices (with n = 11 or 4 units cells) in perpendicular DC and AC magnetic fields. In these model samples, the length of the hopping vortex segment is fixed by the thickness of superconducting layers and vortices are disentangled, at least at low DC fields. It is shown that the high UAC values result from the large contribution of the pinning enhanced viscous drag in the conditions of thermally activated, non-diffusive vortex motion at short time scales, where the influence of thermally induced vortex fluctuations on pinning is weak.

  11. Influence of an external magnetic field on the decoherence of a central spin coupled to an antiferromagnetic environment

    NASA Astrophysics Data System (ADS)

    Yuan, Xiao-Zhong; Goan, Hsi-Sheng; Zhu, Ka-Di

    2007-07-01

    Using the spin wave approximation, we study the decoherence dynamics of a central spin coupled to an antiferromagnetic environment under the application of an external global magnetic field. The external magnetic field affects the decoherence process through its effect on the antiferromagnetic environment. It is shown explicitly that the decoherence factor which displays a Gaussian decay with time depends on the strength of the external magnetic field and the crystal anisotropy field in the antiferromagnetic environment. When the strength of the external magnetic field is increased to the critical field point at which the spin flop transition (a first-order quantum phase transition) happens in the antiferromagnetic environment, the decoherence of the central spin reaches its highest point. This result is consistent with several recent quantum phase transition witness studies. The influences of the environmental temperature on the decoherence behaviour of the central spin are also investigated.

  12. Magnetic island and plasma rotation under external resonant magnetic perturbation in the T-10 tokamak

    NASA Astrophysics Data System (ADS)

    Eliseev, L. G.; Ivanov, N. V.; Kakurin, A. M.; Melnikov, A. V.; Perfilov, S. V.

    2015-05-01

    Experimental comparison of the m = 2, n = 1 mode and plasma rotation velocities at q = 2 magnetic surface in a wide range of the mode amplitudes is presented. Phase velocity of the mode rotation is measured with a set of poloidal magnetic field sensors located at the inner side of the vacuum vessel wall. Plasma rotation velocity at the q = 2 magnetic surface in the direction of the mode phase velocity is measured with the heavy ion beam probe diagnostics. In the presence of a static Resonant Magnetic Perturbation (RMP), the rotation is irregular that appears as cyclical variations of the mode and plasma instantaneous velocities. The period of these variations is equal to the period of the mode oscillations. In the case of high mode amplitude, the rotation irregularity of the mode is consistent with the rotation irregularity of the resonant plasma layer. On the contrary, the observed rise of the mode rotation irregularity in the case of low mode amplitude occurs without an increase of the rotation irregularity of the resonant plasma layer. The experimental results are simulated and analyzed with the TEAR code based on the two-fluid MHD approximation. Calculated irregularities of the mode and plasma rotation depend on the mode amplitude similar to the experimental data. For large islands, the rotation irregularity is attributed to oscillations of the electromagnetic torque applied to the resonant plasma layer. For small islands, the deviation of the mode rotation velocity from the plasma velocity occurs due to the effect of finite plasma resistivity.

  13. Interaction of co-propagating jets in the presence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    MacDonald, Michael; Doyle, Hugo; Brambrink, Erik; Crowston, Robert; Drake, R. Paul; Kuranz, Carolyn; Lamb, Don; Koenig, Michel; Kozlowski, Pawel; Marques, Jean-Raphael; Meinecke, Jena; Pelka, Alexander; Ravasio, Alessandra; Reville, Brian; Tzeferacos, Petros; Woosley, Nigel; Gregori, Gianluca; Acsel Collaboration

    2013-10-01

    We observed the interaction of two co-propagating jets in 1 mbar of argon gas in the presence of an external magnetic field at the LULI laser facility. The jets were created by irradiating a 100 μm aluminum foil with two 1.5 ns laser pulses separated by 5 mm, each containing 500 J of 527 nm light. Optical interferometry and schlieren imaging were used to observe the flow of the interacting jets. Additionally, an induction coil was fielded to measure the magnetic field 3 cm from the initiation of the flows. Measurements were made with and without a 0.5 T external magnetic field. Preliminary results and analysis will be presented. The research leading to these results has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement no. 256973. and by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, grant number DE-NA0001840.

  14. H Infinity Control of Magnetic Bearings to Ensure Both System and External Periodic Disturbance Robustness

    NASA Technical Reports Server (NTRS)

    Jiang, Yuhong; Zmood, R. B.

    1996-01-01

    Both self-excited and forced disturbances often lead to severe rotor vibrations in a magnetic bearing systems with long slender shafts. This problem has been studied using the H-infinity method, and stability with good robustness can be achieved for the linearized model of a magnetic bearing when small transient disturbances are applied. In this paper, the H-infinity control method for self-excited and forced disturbances is first reviewed. It is then applied to the control of a magnetic bearing rotor system. In modelling the system, the shaft is first discretized into 18 finite elements and then three levels of condensation are applied. This leads to a system with three masses and three compliant elements which can be described by six state variable coordinates. Simulation of the resultant system design has been performed at speeds up to 10,000 rpm. Disturbances in terms of different initial displacements, initial impulses, and external periodic inputs have been imposed. The simulation results show that good stability can be achieved under these different transient disturbances using the proposed controller while at the same time reducing the sensitivity to external periodic disturbances.

  15. A crawling and drilling microrobot driven by an external oscillating or precessional magnetic field in tubular environments

    NASA Astrophysics Data System (ADS)

    Kim, S. J.; Jang, G. H.; Jeon, S. M.; Nam, J. K.

    2015-05-01

    We propose a crawling and drilling microrobot actuated by an external precessional magnetic field (EPMF) to effectively unclog obstructed blood vessels. Conventional crawling microrobots can only generate crawling motions using an external oscillating magnetic field. The proposed microrobot can generate navigating (crawling) and drilling motions selectively or simultaneously by controlling the EPMFs. We prototyped the proposed microrobot, and conducted several experiments to verify the efficacy of the crawling and drilling ability of the microrobot in a tubular environment.

  16. Development of integrated AC-DC magnetometer using high-Tc SQUID for magnetic properties evaluation of magnetic nanoparticles in solution

    NASA Astrophysics Data System (ADS)

    Mawardi Saari, Mohd; Takagi, Ryuki; Kusaka, Toki; Ishihara, Yuichi; Tsukamoto, Yuya; Sakai, Kenji; Kiwa, Toshihiko; Tsukada, Keiji

    2014-05-01

    We developed an integrated AC-DC magnetometer using a high critical temperature superconducting quantum interference device (high-Tc SQUID) to evaluate the static and dynamic magnetic properties of magnetic nanoparticles (MNPs) in solution. The flux-transformer method consisted of first-order planar and axial differential coils that were constructed for static and dynamic magnetization measurements, respectively. Vibrating-sample and harmonic detection techniques were used to reduce interference from excitation magnetic fields in the static and dynamic magnetization measurements, respectively. Static and dynamic magnetization measurements were performed on commercially available iron oxide nanoparticles in diluted solutions. The magnetic responses increased with the increase in concentration of the solutions in both measurement results. The magnetization curves showed that the diamagnetic signal due to the carrier liquid of the iron oxide nanoparticles existed in a dilute solution. Biasing with a proper DC magnetic field in the dynamic magnetization measurement resulted in improved signals of the second and third harmonics. Therefore, highly sensitive magnetic characterizations of MNPs utilizing the static and dynamic magnetization measurement are possible via the developed system.

  17. Effects of Magnetic Nanoparticles and External Magnetostatic Field on the Bulk Heterojunction Polymer Solar Cells

    SciTech Connect

    Wang, Kai; Yi, Chao; Liu, Chang; Hu, Xiaowen; Chuang, Steven; Gong, Xiong

    2015-03-18

    The price of energy to separate tightly bound electron-hole pair (or charge-transfer state) and extract freely movable charges from low-mobility materials represents fundamental losses for many low-cost photovoltaic devices. In bulk heterojunction (BHJ) polymer solar cells (PSCs), approximately 50% of the total efficiency lost among all energy loss pathways is due to the photogenerated charge carrier recombination within PSCs and low charge carrier mobility of disordered organic materials. To address these issues, we introduce magnetic nanoparticles (MNPs) and orientate these MNPS within BHJ composite by an external magnetostatic field. Over 50% enhanced efficiency was observed from BHJ PSCs incorporated with MNPs and an external magnetostatic field alignment when compared to the control BHJ PSCs. The optimization of BHJ thin film morphology, suppression of charge carrier recombination, and enhancement in charge carrier collection result in a greatly increased short-circuit current density and fill factor, as a result, enhanced power conversion efficiency.

  18. Effects of Magnetic Nanoparticles and External Magnetostatic Field on the Bulk Heterojunction Polymer Solar Cells

    NASA Astrophysics Data System (ADS)

    Wang, Kai; Yi, Chao; Liu, Chang; Hu, Xiaowen; Chuang, Steven; Gong, Xiong

    2015-03-01

    The price of energy to separate tightly bound electron-hole pair (or charge-transfer state) and extract freely movable charges from low-mobility materials represents fundamental losses for many low-cost photovoltaic devices. In bulk heterojunction (BHJ) polymer solar cells (PSCs), approximately 50% of the total efficiency lost among all energy loss pathways is due to the photogenerated charge carrier recombination within PSCs and low charge carrier mobility of disordered organic materials. To address these issues, we introduce magnetic nanoparticles (MNPs) and orientate these MNPS within BHJ composite by an external magnetostatic field. Over 50% enhanced efficiency was observed from BHJ PSCs incorporated with MNPs and an external magnetostatic field alignment when compared to the control BHJ PSCs. The optimization of BHJ thin film morphology, suppression of charge carrier recombination, and enhancement in charge carrier collection result in a greatly increased short-circuit current density and fill factor, as a result, enhanced power conversion efficiency.

  19. Effects of Magnetic Nanoparticles and External Magnetostatic Field on the Bulk Heterojunction Polymer Solar Cells

    PubMed Central

    Wang, Kai; Yi, Chao; Liu, Chang; Hu, Xiaowen; Chuang, Steven; Gong, Xiong

    2015-01-01

    The price of energy to separate tightly bound electron-hole pair (or charge-transfer state) and extract freely movable charges from low-mobility materials represents fundamental losses for many low-cost photovoltaic devices. In bulk heterojunction (BHJ) polymer solar cells (PSCs), approximately 50% of the total efficiency lost among all energy loss pathways is due to the photogenerated charge carrier recombination within PSCs and low charge carrier mobility of disordered organic materials. To address these issues, we introduce magnetic nanoparticles (MNPs) and orientate these MNPS within BHJ composite by an external magnetostatic field. Over 50% enhanced efficiency was observed from BHJ PSCs incorporated with MNPs and an external magnetostatic field alignment when compared to the control BHJ PSCs. The optimization of BHJ thin film morphology, suppression of charge carrier recombination, and enhancement in charge carrier collection result in a greatly increased short-circuit current density and fill factor, as a result, enhanced power conversion efficiency. PMID:25783755

  20. Mode transition in a planar-coil inductively driven discharge caused by an external magnetic field

    NASA Astrophysics Data System (ADS)

    Demerdzhiev, A.; Tarnev, Kh; Lishev, St.; Shivarova, A.

    2015-02-01

    A hydrogen discharge inductively driven by a planar coil is studied by employing the phase resolved optical emission spectroscopy method, which permits observations not only on the stationary discharge structure but also of its time evolution over the cycle of the rf signal producing the discharge. Since the discharge is considered as a single element of a matrix source of negative hydrogen ions, it is equipped with an extraction device forming an additional grounded metal wall on the side opposite to that where the coil is positioned. Regarding use of a magnetic filter (a localized external magnetic field), the modifications in the discharge caused by the magnetic field have been studied. The results show: (i) transition of the discharge from a capacitive mode to an inductive one with the shift of the magnetic filter from the extraction device towards the coil, (ii) asymmetry both of the stationary and time-varying discharge structure of the inductive mode caused, respectively, by a diamagnetic drift and an ≤ft({\\tilde{E}} × B\\right) -drift in the rf field, (iii) formation in the capacitive mode of the discharge of two electron beams, starting from the position of the magnetic filter, in addition to the beams well known as electron acceleration at the wall sheath expansion and (iv) asymmetry in the structure of the capacitive mode due to ≤ft(E× B\\right) -drifts in the dc and rf fields.

  1. Relativistic Runaway Electron Avalanches in the Presence of an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Cramer, E. S.; Dwyer, J. R.; Liu, N.; Rassoul, H.; Briggs, M. S.

    2015-12-01

    Relativistic runaway electron avalanches are known to be produced inside the high electric field regions of thunderstorms. In this work, we include the effects of an external static magnetic field. Previous studies have shown that the magnetic field has a great influence on the electron motion at higher altitudes, e.g. Lehtinen et al., 1997, and Gurevich et al., 1996. This result proves important when studying phenomena such as Terrestrial Gamma-ray Flashes, and their effects on the upper atmosphere. Therefore, electron avalanche rates, feedback rates, and electron energy distribution functions will be analyzed and compared to the results of previous studies that did not include a magnetic field. The runaway electron avalanche model (REAM) is a Monte Carlo code that simulates the generation, interactions, and propagation of relativistic runaway electrons in air [Dwyer, 2003, 2004, 2007]. We use this simulation for varying strengths and angles between the electric and magnetic fields to calculate avalanche lengths and angular distribution functions of the relativistic runaway electrons. We will also show electron distribution functions in momentum space. Finally, we will discuss the important regimes for which the magnetic field becomes significant in studying the properties of runaway electron avalanches and relativistic feedback.

  2. Total AC loss study of 2G HTS coils for fully HTS machine applications

    NASA Astrophysics Data System (ADS)

    Zhang, Min; Yuan, Weijia; Kvitkovic, Jozef; Pamidi, Sastry

    2015-11-01

    The application of HTS coils for fully HTS machines has become a new research focus. In the stator of an electrical machine, HTS coils are subjected to a combination of an AC applied current and AC external magnetic field. There is a phase shift between the AC current and AC magnetic field. In order to understand and estimate the total AC loss of HTS coils for electrical machines, we designed and performed a calorimetric measurement for a 2G HTS racetrack coil. Our measurement indicates that the total AC loss is greatly influenced by the phase shift between the applied current and the external magnetic field when the magnetic field is perpendicular to the tape surface. When the applied current and the external magnetic field are in phase, the total AC loss is the highest. When there is a 90 degree phase difference, the total AC loss is the lowest. In order to explain this phenomenon, we employ H formulation and finite element method to model the 2G HTS racetrack coil. Our calculation agrees well with experimental measurements. Two parameters are defined to describe the modulation of the total AC loss in terms of phase difference. The calculation further reveals that the influence of phase difference varies with magnetic field direction. The greatest influence of phase difference is in the perpendicular direction. The study provides key information for large-scale 2G HTS applications, e.g. fully HTS machines and superconducting magnetic energy storage, where the total AC loss subjected to both applied currents and external magnetic fields is a critical parameter for the design.

  3. Magnetic island and plasma rotation under external resonant magnetic perturbation in the T-10 tokamak

    SciTech Connect

    Eliseev, L. G.; Ivanov, N. V. Kakurin, A. M.; Perfilov, S. V.; Melnikov, A. V.

    2015-05-15

    Experimental comparison of the m = 2, n = 1 mode and plasma rotation velocities at q = 2 magnetic surface in a wide range of the mode amplitudes is presented. Phase velocity of the mode rotation is measured with a set of poloidal magnetic field sensors located at the inner side of the vacuum vessel wall. Plasma rotation velocity at the q = 2 magnetic surface in the direction of the mode phase velocity is measured with the heavy ion beam probe diagnostics. In the presence of a static Resonant Magnetic Perturbation (RMP), the rotation is irregular that appears as cyclical variations of the mode and plasma instantaneous velocities. The period of these variations is equal to the period of the mode oscillations. In the case of high mode amplitude, the rotation irregularity of the mode is consistent with the rotation irregularity of the resonant plasma layer. On the contrary, the observed rise of the mode rotation irregularity in the case of low mode amplitude occurs without an increase of the rotation irregularity of the resonant plasma layer. The experimental results are simulated and analyzed with the TEAR code based on the two-fluid MHD approximation. Calculated irregularities of the mode and plasma rotation depend on the mode amplitude similar to the experimental data. For large islands, the rotation irregularity is attributed to oscillations of the electromagnetic torque applied to the resonant plasma layer. For small islands, the deviation of the mode rotation velocity from the plasma velocity occurs due to the effect of finite plasma resistivity.

  4. Laser-Plasma Interaction in Presence of an Obliquely External Magnetic Field: Application to Laser Fusion without Radioactivity

    NASA Astrophysics Data System (ADS)

    Mobaraki, M.; Jafari, S.

    2016-08-01

    In this paper, the nonlinear interaction of ultra-high power laser beam with fusion plasma at relativistic regime in the presence of obliquely external magnetic Geld has been studied. Imposing an external magnetic Geld on plasma can modify the density profile of the plasma so that the thermal conductivity of electrons reduces which is considered to be the decrease of the threshold energy for ignition. To achieve the fusion of Hydrogen-Boron (HB) fuel, the block acceleration model of plasma is employed. Energy production by HB isotopes can be of interest, since its reaction does not generate radioactive tritium. By using the inhibit factor in the block model acceleration of plasma and Maxwell's as well as the momentum transfer equations, the electron density distribution and dielectric permittivity of the plasma medium are obtained. Numerical results indicate that with increasing the intensity of the external magnetic field, the oscillation of the laser magnetic field decreases, while the dielectric permittivity increases. Moreover, the amplitude of the electron density becomes highly peaked and the plasma electrons are strongly bunched with increasing the intensity of external magnetic field. Therefore, the magnetized plasma can act as a positive focusing lens to enhance the fusion process. Besides, we find that with increasing θ-angle (from oblique external magnetic field) between 0 and 90°, the dielectric permittivity increases, while for θ between 90° and 180°, the dielectric permittivity decreases with increasing θ.

  5. Inhibiting Klein Tunneling in a Graphene p-n Junction without an External Magnetic Field.

    PubMed

    Oh, Hyungju; Coh, Sinisa; Son, Young-Woo; Cohen, Marvin L

    2016-07-01

    We study by first-principles calculations a densely packed island of organic molecules (F_{4}TCNQ) adsorbed on graphene. We find that with electron doping the island naturally forms a p-n junction in the graphene sheet. For example, a doping level of ∼3×10^{13}  electrons per cm^{2} results in a p-n junction with an 800 meV electrostatic potential barrier. Unlike in a conventional p-n junction in graphene, in the case of the junction formed by an adsorbed organic molecular island we expect that the Klein tunneling is inhibited, even without an applied external magnetic field. Here Klein tunneling is inhibited by the ferromagnetic order that spontaneously occurs in the molecular island upon doping. We estimate that the magnetic barrier in the graphene sheet is around 10 mT. PMID:27419583

  6. Holes localized in nanostructures in an external magnetic field: g-factor and mixing of states

    SciTech Connect

    Semina, M. A.; Suris, R. A.

    2015-06-15

    The energy spectrum and wave functions of holes in the valence band in semiconductor nanosystems, including quantum wells, quantum wires, and quantum dots, in an external magnetic field are theoretically investigated. The dependence of Zeeman splitting of the hole ground state upon variation in the size-quantization parameters with regard to the complex structure of the valence band and magnetic field-induced mixing of hole states is traced. Analytical formulas for describing the Zeeman effect in the valence band in the limiting cases of a quantum disk, spherically symmetric quantum dot, and quantum wire are presented. It is demonstrated that the g-factor of a hole is extremely sensitive to the hole-state composition (heavy or light hole) and, consequently, to the geometry of the size-quantization potential.

  7. Modeling of intense charged particle bunch dynamics in external magnetic fields

    NASA Astrophysics Data System (ADS)

    Barminova, H. Y.; Saratovskyh, M. S.

    2015-09-01

    Program module CAMFT is developed to simulate the intense charged particle bunch dynamics in external magnetic fields. The program is based on the accurate solution of the motion equation for each particle of the intense bunch. The program is written on C++ language and uses standart OpenMP (version 2.0) for parallelization, so one can simulate the behavior of the bunch with intensity about 109-1010 particles. Visual C++ and library Qt 4.8.3 of qtcreator are used for the result visualization. Dynamics of the bunch with arbitrary phase distributions in magnetic fields of arbitrary geometry may be studied by means of the program. The actual CAMFT version is checked while simulating the accelerating structure with racetrack geometry. Modified CAMFT version is checked for ITEP Heavy-Ion Prototype charge-state separator.

  8. Influence of external magnetic field on laser-induced gold nanoparticles fragmentation

    NASA Astrophysics Data System (ADS)

    Serkov, A. A.; Rakov, I. I.; Simakin, A. V.; Kuzmin, P. G.; Shafeev, G. A.; Mikhailova, G. N.; Antonova, L. Kh.; Troitskii, A. V.; Kuzmin, G. P.

    2016-08-01

    Laser-assisted fragmentation is an efficient method of the nanoparticles size and morphology control. However, its exact mechanisms are still under consideration. One of the remaining problems is the plasma formation, inevitably occurring upon the high intensity laser irradiation. In this Letter, the role of the laser-induced plasma is studied via introduction of high-intensity external magnetic field (up to 7.5 T). Its presence is found to cause the plasma emission to start earlier regarding to a laser pulse, also increasing the plume luminosity. Under these conditions, the acceleration of nanoparticles fragmentation down to a few nanometers is observed. Laser-induced plasma interaction with magnetic field and consequent energy transfer from plasma to nanoparticles are discussed.

  9. Shielding of External Magnetic Perturbations By Torque In Rotating Tokamak Plasmas

    SciTech Connect

    Park, Jong-Kyu; Boozer, Allen H.; Menard, Jonathan E.; Gerhardt, Stefan P.; Sabbagh, Steve A.

    2009-08-24

    The imposition of a nonaxisymmetric magnetic perturbation on a rotating tokamak plasma requires energy and toroidal torque. Fundamental electrodynamics implies that the torque is essentially limited and must be consistent with the external response of a plasma equilibrium ƒ = j x B. Here magnetic measurements on National Spherical Torus eXperiment (NSTX) device are used to derive the energy and the torque, and these empirical evaluations are compared with theoretical calculations based on perturbed scalar pressure equilibria ƒ = ∇p coupled with the theory of nonambipolar transport. The measurement and the theory are consistent within acceptable uncertainties, but can be largely inconsistent when the torque is comparable to the energy. This is expected since the currents associated with the torque are ignored in scalar pressure equilibria, but these currents tend to shield the perturbation.

  10. Combined Molecular Dynamics-Spin Dynamics Simulation of α-Iron in an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Mudrick, Mark; Perera, Dilina; Landau, David P.

    Using an atomistic model that treats both translational and spin degrees of freedom, combined molecular and spin dynamics simulations have been performed to study dynamic properties of α-iron. Atomic interactions are described by an empirical many-body potential while spin-spin interactions are handled with a Heisenberg-like Hamiltonian with a coordinate dependent exchange interaction. Each of these interactions are parameterized by first-principles calculations. These simulations numerically solve equations of motion using an algorithm based on the second-order Suzuki-Trotter decomposition for the time evolution operator. Through calculation of the Fourier transform of space-displaced time-displaced correlation functions, vibrational and magnetic excitations have been studied. The application of an external magnetic field up to 10-T has now been included and has been shown to increase the characteristic frequencies of the single-spin-wave excitations. Two-spin-wave interactions have also been investigated.

  11. The effect of external magnetic field on the Raman peaks in manganites

    SciTech Connect

    Sahu, A. K.; Rout, G. C.

    2014-04-24

    We report here a microscopic theoretical model study exhibiting the effect of external magnetic field on the Raman excitation peaks in the CMR manganite system. The Hamiltonian consists of Jahn-Teller (J-T) distortion in e{sub g} band, the double exchange interaction and the Heisenberg spin-spin interaction. Further the phonons are coupled to e{sub g} band electrons, J-T distorted e{sub g} band and the double exchange interaction. The Raman spectral intensity is calculated from the imaginary part of the phonon Green function. The spectra exhibits three peaks besides a very weak high energy peak. The magnetic field effect on these peaks are reported.

  12. Helical plasma striations in liners in the presence of an external axial magnetic field

    NASA Astrophysics Data System (ADS)

    Atoyan, L.; Hammer, D. A.; Kusse, B. R.; Byvank, T.; Cahill, A. D.; Greenly, J. B.; Pikuz, S. A.; Shelkovenko, T. A.

    2016-02-01

    Awe et al. found on the 20 MA Z machine [Acta Phys. Pol. A 115, 956 (2009)] that applying an externally generated axial magnetic field to an imploding liner leads to a helical pattern in the liner when viewed with soft x-ray radiography ([Phys. Rev. Lett. 111, 235005 (2013)] and [Phys. Plasmas 21, 056303 (2014)]). Here, we show that this phenomenon is also observed in extreme ultraviolet self-emission images of 10 mm long cylindrical metal liners having varying diameters and varying wall thicknesses on a 1 MA, 100-200 ns pulsed power generator. The magnetic field in these experiments is created using either twisted return current wires positioned close to the liner, generating a time-varying Bz, or a Helmholtz coil, generating a steady-state Bz.

  13. Inhibiting Klein Tunneling in a Graphene p -n Junction without an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Oh, Hyungju; Coh, Sinisa; Son, Young-Woo; Cohen, Marvin L.

    2016-07-01

    We study by first-principles calculations a densely packed island of organic molecules (F4TCNQ ) adsorbed on graphene. We find that with electron doping the island naturally forms a p -n junction in the graphene sheet. For example, a doping level of ˜3 ×1013 electrons per cm2 results in a p -n junction with an 800 meV electrostatic potential barrier. Unlike in a conventional p -n junction in graphene, in the case of the junction formed by an adsorbed organic molecular island we expect that the Klein tunneling is inhibited, even without an applied external magnetic field. Here Klein tunneling is inhibited by the ferromagnetic order that spontaneously occurs in the molecular island upon doping. We estimate that the magnetic barrier in the graphene sheet is around 10 mT.

  14. Implementation of Kohn's theorem for the ellipsoidal quantum dot in the presence of external magnetic field

    NASA Astrophysics Data System (ADS)

    Hayrapetyan, D. B.; Kazaryan, E. M.; Sarkisyan, H. A.

    2016-01-01

    An electron gas in a strongly oblated ellipsoidal quantum dot with impenetrable walls in the presence of external magnetic field is considered. Influence of the walls of the quantum dot is assumed to be so strong in the direction of the minor axis (the OZ axis) that the Coulomb interaction between electrons in this direction can be neglected and considered as two-dimensional. On the basis of geometric adiabaticity we show that in the case of a few-particle gas a powerful repulsive potential of the quantum dot walls has a parabolic form and localizes the gas in the geometric center of the structure. Due to this fact, conditions occur to implement the generalized Kohn theorem for this system. The parabolic confinement potential depends on the geometry of the ellipsoid, which allows, together with the magnetic field to control resonance frequencies of transitions by changing the geometric dimensions of the QD.

  15. Plasma Jets Subject to Adjustable Current Polarities and External Magnetic Fields

    NASA Astrophysics Data System (ADS)

    Byvank, Tom; Schrafel, Peter; Gourdain, Pierre; Seyler, Charles; Kusse, Bruce

    2014-10-01

    In the present research, collimated plasma jets form from ablation of a radial foil (Al 20 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform external field (1-1.5 T) and under a change of current polarities, which correspond to current moving either radially outward or inward from the foil's central axis. Experimental results are compared with numerical simulations (PERSEUS). The influence of the Hall effect on the jet development is observed under opposite current polarities. Additionally, the magnetic field compression within the jet is examined. Further studies will compare the laboratory-generated plasma jets and astrophysical jets with embedded magnetic fields.

  16. The effect of external magnetic field on plasma acceleration in electromagnetic railgun channel

    NASA Astrophysics Data System (ADS)

    Bobashev, S. V.; Zhukov, B. G.; Kurakin, R. O.; Ponyaev, S. A.; Reznikov, B. I.

    2016-03-01

    We have studied the effect of an external magnetic field on the dynamics of a free plasma piston (PP) accelerated without solid striker armature in an electromagnetic railgun channel filled with various gases (argon or helium). It is established that, as the applied magnetic field grows, the velocity of a shock wave generated by PP in the channel increases. The experimental results are compared to a theoretical model that takes into account the gas pressure force behind the shock wave and the drag force that arises when erosion mass entering the channel is partly entrained by the accelerated plasma. The results of model calculations are in satisfactory agreement with experimental data. The discrepancy somewhat increases with the applied field, but the maximum deviation still does not exceed 20%.

  17. Inductive heat property of Fe3O4/polymer composite nanoparticles in an ac magnetic field for localized hyperthermia.

    PubMed

    Zhao, Dong-Lin; Zhang, Hai-Long; Zeng, Xian-Wei; Xia, Qi-Sheng; Tang, Jin-Tian

    2006-12-01

    The magnetite (Fe(3)O(4)) nanoparticles were prepared by coprecipitation of Fe(3+) and Fe(2+) with an aqueous NaOH solution. The Fe(3)O(4)/polyaniline (PANI) magnetic composite nanoparticles with a core-shell structure with a diameter of 30-50 nm were prepared via an in situ polymerization of aniline in an aqueous solution containing the Fe(3)O(4) magnetic fluid. The inductive heat property of Fe(3)O(4)/PANI composite nanoparticles in an alternating current (ac) magnetic field was investigated. The potential of Fe(3)O(4)/PANI nanoparticles was evaluated for localized hyperthermia treatment of cancers. The saturation magnetization, M(s), and coercivity, H(c), are 50.05 emu g(-1) and 137 Oe for Fe(3)O(4) nanoparticles and 26.34 emu g(-1) and 0 Oe for Fe(3)O(4)/PANI composite nanoparticles, respectively. Exposed in the ac magnetic field for 29 min, the temperatures of physiological saline suspensions containing Fe(3)O(4) nanoparticles or Fe(3)O(4)/PANI composite nanoparticles are 63.6 degrees C and 52.4 degrees C, respectively. The Fe(3)O(4)/PANI composite nanoparticles would be useful as good thermoseeds for localized hyperthermia treatment of cancers. PMID:18458406

  18. Gyrokinetic simulations with external resonant magnetic perturbations: Island torque and nonambipolar transport with plasma rotation

    NASA Astrophysics Data System (ADS)

    Waltz, R. E.; Waelbroeck, F. L.

    2012-03-01

    Static external resonant magnetic field perturbations (RMPs) have been added to the gyrokinetic code GYRO [J. Candy and R. E. Waltz, J. Comp. Phys. 186, 545 (2003)]. This allows nonlinear gyrokinetic simulations of the nonambipolar radial current flow jr, and the corresponding j→×B→ plasma torque (density) R[jrBp/c], induced by magnetic islands that break the toroidal symmetry of a tokamak. This extends the previous GYRO formulation for the transport of toroidal angular momentum (TAM) [R. E. Waltz, G. M. Staebler, J. Candy, and F. L. Hinton, Phys. Plasmas 14, 122507 (2007); errata 16, 079902 (2009)]. The focus is on electrostatic full torus radial slice simulations of externally induced q =m/n=6/3 islands with widths 5% of the minor radius or about 20 ion gyroradii. Up to moderately strong E ×B rotation, the island torque scales with the radial electric field at the resonant surface Er, the island width w, and the intensity I of the high-n micro-turbulence, as Erw√I . The radial current inside the island is carried (entirely in the n =3 component) and almost entirely by the ion E ×B flux, since the electron E ×B and magnetic flutter particle fluxes are cancelled. The net island torque is null at zero Er rather than at zero toroidal rotation. This means that while the expected magnetic braking of the toroidal plasma rotation occurs at strong co- and counter-current rotation, at null toroidal rotation, there is a small co-directed magnetic acceleration up to the small diamagnetic (ion pressure gradient driven) co-rotation corresponding to the zero Er and null torque. This could be called the residual stress from an externally induced island. At zero Er, the only effect is the expected partial flattening of the electron temperature gradient within the island. Finite-beta GYRO simulations demonstrate almost complete RMP field screening and n =3 mode unlocking at strong Er.

  19. Cancellation technique of external noise inside a magnetically shielded room used for biomagnetic measurements

    NASA Astrophysics Data System (ADS)

    Kandori, Akihiko; Miyashita, Tsuyoshi; Tsukada, Keiji

    2000-05-01

    First-order gradiometers inside a magnetically shielded room (MSR) were used to cancel magnetic-field noise. However, the magnetic field inside a MSR is distorted when the amount of external noise is large. This distortion is caused by the low-pass filter property of the MSR. Therefore, the time constants of the frequency-dependent attenuation of the MSR vary spatially and this variation must be taken into account. To investigate noise cancellation, we used a multichannel superconducting quantum interference device consisting of four gradiometers measuring a source signal and two gradiometers as a reference. To compensate for the different magnitudes of the gradiometer wave forms, which differed because of slight differences in their pickup-coil cancel rates, we calculated a fitting parameter. The noise-cancellation method consisted of two processes: reduction of ambient noise caused by the differences in the cancel rate of the gradiometers and a gradient magnetic field inside the MSR, and cancellation of wave-form distortion caused by the spatial variation of the time constants inside the MSR. This cancellation method provides additional attenuation of over 20-30 dB in addition to the balance (>46 dB) of a first-order gradiometer. However, the remaining noise, especially a spike (<2 pT) at the beginning of a large ambient noise step, could not be completely canceled. This noise was caused by the slight difference between the time constants at the reference sensor position and at the signal sensor position. Except for this noise spike, however, the noise cancellation enabled clear magnetocardiogram wave forms to be measured without being affected by strong external noise.

  20. Control of a Bose-Einstein condensate on a chip by external optical and magnetic potentials

    SciTech Connect

    Maluckov, A.; Petrovic, J.; Gligoric, G.; Hadzievski, Lj.; Lombardi, P.; Schaefer, F.; Cataliotti, F.S.

    2012-09-15

    In this paper we explore the possibilities of control of a Bose-Einstein condensate on an atom chip by the use of potentials generated by photonic and magnetic components. We show that the fields produced by both types of components can be modelled by a generic exponential potential and derive analytic expressions that allow for an easy assessment of their impact on a trapped condensate. Using dynamical numerical simulations we study the transport of the condensate between the control structures on a chip. We study in detail different regimes of the condensate behaviour in an evanescent light potential generated by a photonic structure in the vicinity of the condensate and in magnetic potentials generated by a wire or a coil. The calculations are based on the reported parameters of atom chip setups and available photonic and magnetic components. Finally, the model is verified by an experiment with a condensate on an atom chip and a coil. - Highlights: Black-Right-Pointing-Pointer Generic potential used to describe both the optical evanescent and magnetic fields. Black-Right-Pointing-Pointer An analytic closed form solution found for the impact of a generic potential on a BEC. Black-Right-Pointing-Pointer BEC dynamics calculated for potential time sequences attainable in experiments. Black-Right-Pointing-Pointer Conditions for BEC transfer by an external field identified. Black-Right-Pointing-Pointer Exponential-potential model validated by a BEC-on-chip experiment.

  1. Critical Current Test of Liquid Hydrogen Cooled HTC Superconductors under External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Shirai, Yasuyuki; Shiotsu, Masahiro; Tatsumoto, Hideki; Kobayashi, Hiroaki; Naruo, Yoshihiro; Nonaka, Satoshi; Inatani, Yoshifumi

    High-Tc (HTC) superconductors including MgB2 will show excellent properties under temperature of Liquid Hydrogen (LH2:20K), which has large latent heat and low viscosity coefficient. In order to design and fabricate the LH2 cooled superconducting energy devices, we must clear the cooling property of LH2 for superconductors, the cooling system and safety design of LH2 cooled superconducting devices and electro-magnetic property evaluation of superconductors (BSCCO, REBCO and MgB2) and their magnets cooled by LH2. As the first step of the study, an experimental setup which can be used for investigating heat transfer characteristics of LH2 in a pool and also in forced flow (circulation loop with a pump), and also for evaluation of electro-magnetic properties of LH2 cooled superconductors under external magnetic field (up to 7 T). In this paper, we will show a short sketch of the experimental set-up, practical experiences in safety operation of liquid hydrogen cooling system and example test results of critical current evaluation of HTC superconductors cooled by LH2.

  2. Magnetic nanobeads present during enzymatic amplification and labeling for a simplified DNA detection protocol based on AC susceptometry

    NASA Astrophysics Data System (ADS)

    Bejhed, Rebecca S.; Strømme, Maria; Svedlindh, Peter; Ahlford, Annika; Strömberg, Mattias

    2015-12-01

    Magnetic biosensors are promising candidates for low-cost point-of-care biodiagnostic devices. For optimal efficiency it is crucial to minimize the time and complexity of the assay protocol including target recognition, amplification, labeling and read-out. In this work, possibilities for protocol simplifications for a DNA biodetection principle relying on hybridization of magnetic nanobeads to rolling circle amplification (RCA) products are investigated. The target DNA is recognized through a padlock ligation assay resulting in DNA circles serving as templates for the RCA process. It is found that beads can be present during amplification without noticeably interfering with the enzyme used for RCA (phi29 polymerase). As a result, the bead-coil hybridization can be performed immediately after amplification in a one-step manner at elevated temperature within a few minutes prior to read-out in an AC susceptometer setup, i.e. a combined protocol approach. Moreover, by recording the phase angle ξ = arctan(χ″/χ'), where χ and χ″ are the in-phase and out-of-phase components of the AC susceptibility, respectively, at one single frequency the total assay time for the optimized combined protocol would be no more than 1.5 hours, often a relevant time frame for diagnosis of cancer and infectious disease. Also, applying the phase angle method normalization of AC susceptibility data is not needed. These findings are useful for the development of point-of-care biodiagnostic devices relying on bead-coil binding and magnetic AC susceptometry.

  3. A study of the effect of an external magnetic field on the resonant frequency of magnetic fluids

    NASA Astrophysics Data System (ADS)

    Fannin, P. C.; Charles, S. W.; Relihan, T.

    1996-09-01

    The complex magnetic susceptibility, χ( ω) = χ'( ω) - i χ″( ω), of two magnetic fluids has been measured over the frequency range 0.1 to 6 GHz, and ferromagnetic resonance observed, indicated by the real component of the susceptibility going negative at a frequency, fres. In this study the dependence of fres, on the presence of an external magnetic field, H, in the approximate range 0 to 68 KA/m has been examined for colloidal suspensions of magnetite particles and cobalt particles in isopar M. In both cases, plots of this dependence are found to be linear with slopes having values of the magnetogyric ratio, γ, within experimental error. These plots enable the average value of the internal anisotropy field, overlineHA, to be measured, from which mean values of the magnetic anisotropy constant of the particles, overlineK, are derived. The experimental profiles of χ'(ω) and χ″(ω), for the magnetite particle system as a function of H, have been fitted to modified equations of Raikher and Shliomis suitably adapted to include a normal distribution of particle energy barriers, KeffV, to the rotation of the magnetic moments. It is found that KeffV varies linearly with increasing H, whilst the standard deviation of the distribution of KeffV decreases with increase in H. The main contribution to the resonant linewidth, Δω, for the larger values of H, arises from the mean random spacial distribution of HA, and is given by γ overlineHA. This is consistent with the experimental observations.

  4. Solar wind control of lunar external magnetic enhancement: A case study

    NASA Astrophysics Data System (ADS)

    Nishino, M. N.; Fujimoto, M.; Tsunakawa, H.; Shibuya, H.; Takahashi, F.; Shimizu, H.; Matsushima, M.; Saito, Y.

    2012-04-01

    We study an interaction between the solar wind (SW) and the magnetic anomalies on the lunar surface using SELENE (Kaguya) data. It has been known that magnetic enhancements are at times detected near the limb external to the lunar wake, which is thus called lunar external magnetic enhancement (LEME), as a result of direct interaction between the SW and the lunar crustal fields. Previous observational studies, based on statistical trends that stronger interplanetary magnetic field (IMF) and higher SW density favor the LEME in high solar zenith angle (SZA) region, suggested a fluid-type interaction as a candidate for formation mechanism of the LEME. However, neither the IMF orientation nor the crustal field direction has not been taken into account in the previous analyses. We show evidence that relation between the IMF and crustal field orientation is also one of the key factors that control the extent of LEME, focusing on one-day observations (12 revolutions) that include data above South Pole-Aitken (SPA) basin which is characterized by strong crustal fields in a wide region. Strong LEMEs are detected at 100 km altitude around SPA basin under the stronger and northward IMF condition, while they weakens under southward IMF. We examined the crustal field model (uncompressed by the SW) constructed from the SELENE magnetometer data to know the orientation of the crustal field at 300 km, 100 km, and lower altitude. In the region where the peak of the magnetic enhancement is detected at 100 km altitude, the model crustal field at 300 km altitude is directed northward, while the model field at 100 km and lower altitude had a southward component in some revolutions. This suggests that the lunar crustal field is compressed by the SW dynamic pressure, and that its large scale component is essential to the formation of the LEME. In addition, our results show that pile-up of the IMF above the crustal fields becomes more effective under parallel field configuration, and

  5. Angular Dependence of Transport AC Losses in Superconducting Wire with Position-Dependent Critical Current Density in a DC Magnetic Field

    NASA Astrophysics Data System (ADS)

    Su, Xing-liang; Xiong, Li-ting; Gao, Yuan-wen; Zhou, You-he

    2013-07-01

    Transport AC losses play a very important role in high temperature superconductors (HTSs), which usually carry AC transport current under applied magnetic field in typical application-like conditions. In this paper, we propose the analytical formula for transport AC losses in HTS wire by considering critical current density of both inhomogeneous and anisotropic field dependent. The angular dependence of critical current density is described by effective mass theory, and the HTS wire has inhomogeneous distribution cross-section of critical current density. We calculate the angular dependence of normalized AC losses under different DC applied magnetic fields. The numerical results of this formula agree well with the experiment data and are better than the results of Norris formula. This analytical formula can explain the deviation of experimental transport current losses from the Norris formula and apply to calculate transport AC losses in realistic practical condition.

  6. Quasi-TEM electromagnetic modes of a plasma waveguide with a nonsimply connected cross section in an external magnetic field

    SciTech Connect

    Kartashov, I. N. Kuzelev, M. V.

    2014-12-15

    Electromagnetic modes of a plasma waveguide with a nonsimply connected cross section in an external magnetic field are investigated. The existence of quasi-TEM modes in a finite-strength magnetic field is demonstrated. It is shown that, in the limits of infinitely strong and zero magnetic fields, this mode transforms into a true TEM mode. The possibility of excitation of such modes by an electron beam in the regime of the anomalous Doppler effect is analyzed.

  7. Assessing Variability in the Earth's External and Induced Magnetic Field Using Ground-Based Magnetic Field Measurements

    NASA Astrophysics Data System (ADS)

    Wild, J. A.; Dorrian, G.; Freeman, M. P.; Gjerloev, J. W.; Honary, F.; Shore, R. M.

    2013-12-01

    Electrical currents in the upper atmosphere and near-Earth Space (and the currents induced by these in the oceans, crust, and mantle) give rise to the Earth's external and induced magnetic field (EIMF). We present a study of the variation of the EIMF over the Earth's surface based on controlling factors such as season, solar activity, and solar wind conditions. Our analysis is based on the unprecedentedly large and relatively homogeneous set of global magnetic field measurements available via the international SuperMAG program. SuperMAG has compiled a standardised set of EIMF data from over 300 stations since 1997 involving rotation into a single coordinate system, the removal of the main field, and identification of artefacts and errors. In our analysis, variation of the EIMF over the Earth's surface is calculated by dividing the data into a regular spatial grid and calculating the average magnetic vector at each location, based on the prevailing controlling factors. As well as discussing the average EIMF under different driving conditions, we investigate the variability in the EIMF from these averaged configurations during specific events.

  8. Simulation of magnetic drug targeting through tracheobronchial airways in the presence of an external non-uniform magnetic field using Lagrangian magnetic particle tracking

    NASA Astrophysics Data System (ADS)

    Pourmehran, O.; Rahimi-Gorji, M.; Gorji-Bandpy, M.; Gorji, T. B.

    2015-11-01

    Drug delivery technologies are an important area within biomedicine. Targeted drug delivery aims to reduce the undesired side effects of drug usage by directing or capturing the active agents near a desired site within the body. Herein, a numerical investigation of magnetic drug targeting (MDT) using aerosol drugs named polystyrene particle (PMS40) in human lung is presented considering one-way coupling on the transport and capture of the magnetic particle. A realistic 3D geometry based on CT scan images is provided for CFD simulation. An external non-uniform magnetic field is applied. Parametric investigation is conducted and the influence of particle diameter, magnetic source position, and magnetic number (Mn) on the deposition efficiency and particle behavior is reported. According to the results, the magnetic field increased deposition efficiency of particles in a target region, the efficiency of deposition and MDT technique has a direct relation with increasing the particle diameter for magnetic number of 1 Tesla (T) and lower (Mn≤1(T)). Also it can be seen that there is an inverse relation between the particle diameter and deposition efficiency when Mn is more than 1 (T).

  9. A New Approach to Isolating External Magnetic Field Components in Spacecraft Measurements of the Earth's Magnetic Field Using Global Positioning System observables

    NASA Technical Reports Server (NTRS)

    Raymond, C.; Hajj, G.

    1994-01-01

    We review the problem of separating components of the magnetic field arising from sources in the Earth's core and lithosphere, from those contributions arising external to the Earth, namely ionospheric and magnetospheric fields, in spacecraft measurements of the Earth's magnetic field.

  10. Self-propagating high-temperature synthesis of metal oxides; Reactions in external magnetic fields

    NASA Astrophysics Data System (ADS)

    Aguas, Marco Diogo

    The preparation of metal oxides by Self-Propagating High-Temperature Synthesis is reported. The reactions are started with a point source of ignition; typically a hot wire. A synthesis wave is observed moving out from the point source and reactions terminate in seconds. Products obtained can be classified into ferrites (magnetic applications) and stannates (gas sensing applications). Ferrites were synthesised under variable external magnetic fields. The synthesis wave is hotter in the presence of an external magnetic field for hard ferrite synthesis. For spinel ferrites the opposite was observed. Materials synthesised in the field show differences in their bulk magnetic properties (coercivity and saturation magnetisation), structures and microstructures. Combustion reactions in large fields revealed changes in unit cell volume (shrinkage was observed for hard ferrites while expansion was observed for spinel ferrites). SHS synthesised hard ferrites show two distinct components; one has large grain structure consisting of 50% acicular particles of 100 mum and another that has a finer microstructure. The ferrites studied were BaFe12O19, SrFe12O19, MgFe2O4, and Mg0.5Zn0.5Fe2O4. Formation of ferrites by SHS was also studied by time resolved X-ray diffraction. Patterns were successfully recorded at up to 0.8 s intervals. These showed that synthesis of ferrites is in some cases through intermediates. TRXRD has also helped form theories for the mechanistic pathways of the reactions. Work carried out has shown that magnetic fields act on SHS reactions in 3 stages; before, during and after reactions. BaSnO3 was prepared by SHS from various barium and tin reagents. Sintering of the SHS prepared powders at 800 °C for 2-72 h produced phase pure BaSnO3. Powders obtained showed sensitivity towards CO2. All products were analysed by X-ray powder diffraction, SEM/ED AX, electron microprobe, and FT-IR. The ferrites were also analysed by 57Fe Mossbauer spectroscopy, VSM, thermal

  11. Liquid phase electroepitaxial bulk growth of binary and ternary alloy semiconductors under external magnetic field

    NASA Astrophysics Data System (ADS)

    Sheibani, Hamdi

    2002-01-01

    Liquid Phase Electroepitaxy (LPEE) and is a relatively new, promising technique for producing high quality, thick compound semiconductors and their alloys. The main objectives are to reduce the adverse effect of natural convection and to determine the optimum growth conditions for reproducible desired crystals for the optoelectronic and electronic device industry. Among the available techniques for suppressing the adverse effect of natural convection, the application of an external magnetic field seems the most feasible one. The research work in this dissertation consists of two parts. The first part is focused on the design and development of a state of the art LPEE facility with a novel crucible design, that can produce bulk crystals of quality higher than those achieved by the existing LPEE system. A growth procedure was developed to take advantage of this novel crucible design. The research of the growth of InGaAs single crystals presented in this thesis will be a basis for the future LPEE growth of other important material and is an ideal vehicle for the development of a ternary crystal growth process. The second part of the research program is the experimental study of the LPEE growth process of high quality bulk single crystals of binary/ternary semiconductors under applied magnetic field. The compositional uniformity of grown crystals was measured by Electron Probe Micro-analysis (EPMA) and X-ray microanalysis. The state-of-the-art LPEE system developed at University of Victoria, because of its novel design features, has achieved a growth rate of about 4.5 mm/day (with the application of an external fixed magnetic field of 4.5 KGauss and 3 A/cm2 electric current density), and a growth rate of about 11 mm/day (with 4.5 KGauss magnetic field and 7 A/cm2 electric current density). This achievement is simply a breakthrough in LPEE, making this growth technique absolutely a bulk growth technique and putting it in competition with other bulk growth techniques

  12. Study of the Dependency on Magnetic Field and Bias Voltage of an AC-Biased TES Microcalorimeter

    NASA Technical Reports Server (NTRS)

    Gottardi, L.; Bruijn, M.; denHartog, R.; Hoevers, H.; deKorte, P.; vanderKuur, J.; Linderman, M.; Adams, J.; Bailey, C.; Bandler, S.; Chervenak, J.; Eckart, M.; Finkbeiner, F.; Kelley, R.; Kilbourne, C.; Porter, F.; Sadlier, J.; Smith, S.

    2012-01-01

    At SRON we are studying the performance of a Goddard Space Flight Center single pixel TES microcalorimeter operated in an AC bias configuration. For x-ray photons at 6 keV the pixel shows an x-ray energy resolution Delta E(sub FWHM) = 3.7 eV, which is about a factor 2 worse than the energy resolution observed in an identical DC-biased pixel. In order to better understand the reasons for this discrepancy we characterized the detector as a function of temperature, bias working point and applied perpendicular magnetic field. A strong periodic dependency of the detector noise on the TES AC bias voltage is measured. We discuss the results in the framework of the recently observed weak-link behaviour of a TES microcalorimeter.

  13. Chaotic behavior of collective ion dynamics in the presence of an external static magnetic field

    NASA Astrophysics Data System (ADS)

    Poria, Swarup; Ghosh, Samiran

    2016-06-01

    The two-dimensional nonlinear collective ion dynamics in the presence of external magnetic field in an electron-ion plasma is investigated. The analysis is performed for traveling plane waves to elucidate the various aspects of the phase-space dynamics. The presence of magnetic field makes the dynamics of the nonlinear wave complex with a complicated phase-space behavior. Thus, the nonlinear wave supports a wide class of nonlinear structures viz., single soliton, multi-soliton, periodic, and quasi-periodic oscillations depending on the values of M (Mach number) and Ω (the ratio of ion gyro-frequency to the ion plasma frequency). The computational results predict the chaotic behavior of the nonlinear wave and the transition to chaos takes place when Ω ≳ 0.35 depending on the direction of propagation and the value of M. The amplitude of the wave depends on the obliqueness of the propagation and Mach number, whereas the magnetic field changes the dispersion properties of the wave.

  14. Superconducting-magnetic heterostructures: a method of decreasing AC losses and improving critical current density in multifilamentary conductors.

    PubMed

    Glowacki, B A; Majoros, M

    2009-06-24

    Magnetic materials can help to improve the performance of practical superconductors on the macroscale/microscale as magnetic diverters and also on the nanoscale as effective pinning centres. It has been established by numerical modelling that magnetic shielding of the filaments reduces AC losses in self-field conditions due to decoupling of the filaments and, at the same time, it increases the critical current of the composite. This effect is especially beneficial for coated conductors, in which the anisotropic properties of the superconductor are amplified by the conductor architecture. However, ferromagnetic coatings are often chemically incompatible with YBa(2)Cu(3)O(7) and (Pb,Bi)(2)Sr(2)Ca(2)Cu(3)O(9) conductors, and buffer layers have to be used. In contrast, in MgB(2) conductors an iron matrix may remain in direct contact with the superconducting core. The application of superconducting-magnetic heterostructures requires consideration of the thermal and electromagnetic stability of the superconducting materials used. On one hand, magnetic materials reduce the critical current gradient across the individual filaments but, on the other hand, they often reduce the thermal conductivity between the superconducting core and the cryogen, which may cause destruction of the conductor in the event of thermal instability. A possible nanoscale method of improving the critical current density of superconducting conductors is the introduction of sub-micron magnetic pinning centres. However, the volumetric density and chemical compatibility of magnetic inclusions has to be controlled to avoid suppression of the superconducting properties. PMID:21828430

  15. Magnetic cylindrical colloids at liquid interfaces exhibit non-volatile switching of their orientation in an external field.

    PubMed

    Newton, Bethany J; Buzza, D Martin A

    2016-06-28

    We study the orientation of magnetic cylindrical particles adsorbed at a liquid interface in an external field using analytical theory and high resolution finite element simulations. Cylindrical particles are interesting since they possess multiple locally stable orientations at the liquid interface so that the orientational transitions induced by an external field will not disappear when the external field is removed, i.e., the switching effect is non-volatile. We show that, in the absence of an external field, as we reduce the aspect ratio α of the cylinders below a critical value (αc≈ 2) the particles undergo spontaneous symmetry breaking from a stable side-on state to one of two equivalent stable tilted states, similar to the spontaneous magnetisation of a ferromagnet going through the Curie point. By tuning both the aspect ratio and contact angle of the cylinders, we show that it is possible to engineer particles that have one, two, three or four locally stable orientations. We also find that the magnetic responses of cylinders with one or two stable states are similar to that of paramagnets and ferromagnets respectively, while the magnetic response of systems with three or four stable states are even more complex and have no analogs in simple magnetic systems. Magnetic cylinders at liquid interfaces therefore provide a facile method for creating switchable functional monolayers where we can use an external field to induce multiple non-volatile changes in particle orientation and self-assembled structure. PMID:27200513

  16. Dynamics of low-density ultracold plasmas in externally applied electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Wilson, Truman M.

    The experiments described in this thesis were focused on the influence of external electric and magnetic fields and electron evaporation on the evolution of ultracold plasmas (UCPs). The UCPs were created from the photoionization of 85Rb which was first captured in a magneto-optical trap (MOT) and then magnetically trapped and transferred by a set of magnetic coils attached to a motorized translation stage to a region of the vacuum chamber with a set of electrodes. The first experiment studied the response of the UCP to sharp electric field pulses, which included 2 cycles of a sine wave pulse. These experiments showed a resonant response to the 2 cycles of rf that was density dependent, but was not a collision based mechanism. Instead, the response was caused by a rapid energy transfer to individual electrons through the collective motion of the electron cloud in the UCP. This density-dependent response allowed us to develop a technique for measuring the expansion rate of the UCPs in our system. It was also observed in second set of experiments that electron evaporation from the UCP had a significant effect on the amount of energy that was transferred to the ions to drive the UCP expansion. Model calculations show that we should expect electron evaporation to have a more significant influence on the UCP expansion rate at the relatively low densities of the UCPs that we create compared to other experiments. By modeling electron evaporation during expansion, our data are consistent with evaporation reducing the electron temperature significantly, which lowers the overall UCP expansion rate. In addition to these studies, we also performed an experiment in which it was observed that in the presence of a magnetic field there was a significant increase in the initial UCP expansion rate coupled with a deceleration of the ion expansion at later times in the UCP evolution. Our observations to date are consistent with the magnetic field influencing electron screening and UCP

  17. Time-resolved magnetic flux and AC-current distributions in superconducting yttrium barium copper oxide thin films and multifilaments

    NASA Astrophysics Data System (ADS)

    Yang, Ran

    Time-resolved magneto-optical imaging (TRMOI) technique allows dynamic ac transport measurements on superconductors. The high time and spatial resolutions of the measurements also offer good quantitative data analysis of the MO images. YBa2Cu 3O7-delta (YBCO) was discovered as a high-temperature superconductor (HTSC) which has wide applications due to its high critical temperature of Tc = 91 K, and high critical current density Jc in the order of 106-7 Acm-2. Many of the applications require high ac current load and a high magnetic field. We study the interaction behavior of YBCO thin films in an ac transport current and a dc magnetic field by the TRMOI technique. In this dissertation, I first introduce the applications of high-temperature superconductors with focus on YBCO and describe the advantages of the TRMOI technique we developed over other methods to map the magnetic flux distribution of superconductors. The theories to understand the magnetic properties of HTSC are presented, followed by theoretical models. I also introduce a newly developed finite elemental method (FEM) simulation which is proved to be a better theoretical guideline to our data analysis. The TRMOI experimental setup and the procedures are discussed in detail. I show step-by-step the calibration of light intensity profiles averaged from MO images to determine magnetic field distribution, and a numerical inversion of the Biot-Savart law to calculate the current density distributions. The current density evolution in YBCO thin films is studied by TRMOI as a function of the phase of an ac current applied simultaneously with a perpendicular dc magnetic field. The measurements show that an ac current enables the vortex matter in YBCO thin films to reorganize into two coexisting steady states of driven vortex motion with different characteristics. To study the transport current effects in YBCO thin films, we present a new empirical method to separate the total current distribution into a

  18. The enigma of apparent symmetry in the internal Saturn magnetic field: clues from external periodic signals

    NASA Astrophysics Data System (ADS)

    Southwood, David; Kivelson, Margaret

    We present a scenario which starts from the well-known periodic cam currents in the middle Saturnian magnetosphere. We point that the currents impose a periodic torque on the planetary ionosphere. We suggest that the simplest manner to explain the reason for the torque is to postulate the presence of relatively massive conducting material somewhere on magnetic shells within the cam shells (at L=10-12). Indeed the inward extension of the cam field magnetic observations suggest it should be near or inside the orbit of Enceladus. The model at the same time would resolve the long-standing puzzle that the all multipole fits to the measured magnetic field at Saturn indicate the internal field to be like an off-set dipole closely aligned with the planetary rotation axis. The apparent internal field axial symmetry has hitherto been proposed to be imposed by conducting layers immediately below the planetary surface at low and mid-latitude which suppress higher order fields that should be present in a dynamo generated field. Here we point out that the conductor responsible for suppressing evidence of non-axisymmetric moments may not be inside the planet and that the cam currents provide an important clue. In the simple case where the planetary dipole is tilted with respect to the rotation axis, conducting material in the equatorial regions should experience a periodic rocking force. Current systems to exert such forces couple the equatorial regions to the ionosphere and the result is a torque between equator and ionosphere. If the conducting material in the magnetosphere is massive enough, a small asymmetric part of the planetary magnetic field may be insufficient to impose the rocking motion in the equatorial region. At Saturn, the role of charged dust in the vicinity of the rings may add considerable inertia to the equatorial plasma, thereby making the proposed scenario plausible in the inner magnetosphere. In the scenario envisaged, the evidence of an internal dipole tilt

  19. Two-Photon Frequency Comb Excitation of Rubidium Atoms in External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Vujičić, N.; Ban, T.; Skenderović, H.; Vdović, S.; Pichler, G.

    2008-10-01

    In the present experiment the 5S-5D two-photon transitions in 85Rb and 87Rb atoms as a result of the interaction of the femtosecond frequency comb with atomic levels of both rubidium isotopes are investigated. The main problem in studying of two-photon transitions is in optimization of the excitation efficiency of the desired state. There are two general cases: those transition with an intermediate resonance those in which the pulse spectrum is far detuned from an intermediate resonance. In order to investigate the dependence of the two-photon fluorescence signal as a result of interaction of the frequency comb with perturbed energy-level pattern an external magnetic field was applied.

  20. High-power microwave amplifier based on overcritical relativistic electron beam without external magnetic field

    SciTech Connect

    Kurkin, S. A. Koronovskii, A. A.; Frolov, N. S.; Hramov, A. E.; Rak, A. O.; Kuraev, A. A.

    2015-04-13

    The high-power scheme for the amplification of powerful microwave signals based on the overcritical electron beam with a virtual cathode (virtual cathode amplifier) has been proposed and investigated numerically. General output characteristics of the virtual cathode amplifier including the dependencies of the power gain on the input signal frequency and amplitude have been obtained and analyzed. The possibility of the geometrical working frequency tuning over the range about 8%–10% has been shown. The obtained results demonstrate that the proposed virtual cathode amplifier scheme may be considered as the perspective high-power microwave amplifier with gain up to 18 dB, and with the following important advantages: the absence of external magnetic field, the simplicity of construction, the possibility of geometrical frequency tuning, and the amplification of relatively powerful microwave signals.

  1. Heat current characteristics in nanojunctions: The effect of external magnetic fields

    NASA Astrophysics Data System (ADS)

    Dominguez, D. Melisa; Restrepo, Juliana; Rodriguez, Boris A.; Chitra, R.

    We study the heat current in the simplest hybrid device of a two level system weakly coupled to two heat baths. We consider both metallic and semiconducting baths with external magnetic fields applied on the central spin and the baths. By using a reduced density matrix approach together with a simple Born-Markov approximation we calculate the heat current. Our goal is to investigate the effect of the applied fields in the transient and steady state heat current, the ensuing rectification and the possibility of using our setup as a building block for a quantum thermal diode. 1This work was supported by the Vicerrectoria de Investigacion of the Universidad Antonio Narino, Colombia under Project Number 20141031 and by COLCIENCIAS under Grant Number 111556934912.

  2. Stability of an electrically induced vortical flow in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Vlasyuk, V. Kh.; Shcherbinin, E. V.

    2004-09-01

    A numerical solution of the Navier-Stokes equations, without any additional and special assumptions, is applied to investigate the stability of electrovortex flows (EVF) and the azimuthal rotation driven by the interaction of a working current with an external magnetic field. The field was induced by one or two rings with the current arranged at the bottom of the cylindrical area under calculation. The current in the second ring was equal to the current in the first one but was opposite in direction. The results obtained are sufficient to analyze qualitatively and quantitatively the occurrence of a non-stationary hydrodynamic stream function and a Taylor instability, when an easier liquid breaks upwards through a denser layer. Critical dependencies on the EVT parameter S and interaction N are found. The main result of the work is the found characteristic reorganization of the zero vorticity line when the parameter approaches a critical value. Figs 6, Refs 15.

  3. Superconductor-Mediated Modification of Gravity? AC Motor Experiments with Bulk YBCO Disks in Rotating Magnetic Fields

    NASA Technical Reports Server (NTRS)

    Noever, David A.; Koczor, Ronald J.; Roberson, Rick

    1998-01-01

    We have previously reported results using a high precision gravimeter to probe local gravity changes in the neighborhood of large bulk-processed high-temperature superconductors. Podkietnov, et al (Podkietnov, E. and Nieminen, R. (1992) A Possibility of Gravitational Force Shielding by Bulk YBa2 Cu3 O7-x Superconductor, Physica C, C203:441-444.) have indicated that rotating AC fields play an essential role in their observed distortion of combined gravity and barometric pressure readings. We report experiments on large (15 cm diameter) bulk YBCO ceramic superconductors placed in the core of a three-phase, AC motor stator. The applied rotating field produces up to a 12,000 revolutions per minute magnetic field. The field intensity decays rapidly from the maximum at the outer diameter of the superconducting disk (less than 60 Gauss) to the center (less than 10 Gauss). This configuration was applied with and without a permanent DC magnetic field levitating the superconducting disk, with corresponding gravity readings indicating an apparent increase in observed gravity of less than 1 x 10(exp -6)/sq cm, measured above the superconductor. No effect of the rotating magnetic field or thermal environment on the gravimeter readings or on rotating the superconducting disk was noted within the high precision of the observation. Implications for propulsion initiatives and power storage flywheel technologies for high temperature superconductors will be discussed for various spacecraft and satellite applications.

  4. Grain in weakly ionized plasma in the presence of an external magnetic field: Charging by plasma currents and effective potential

    SciTech Connect

    Momot, A. I.; M.M. Bogolubov Institute for Theoretical Physics, Nat. Acad. Sci. of Ukraine, 14b, Metrologichna Str., Kyiv, 03680

    2013-07-15

    The problem of grain screening is solved numerically for the case of weakly ionized plasma in the presence of an external magnetic field. The plasma dynamics is described within the drift-diffusion approximation under the assumption that the grain absorbs all encountered electrons and ions. We also assume that the plasma current through the grain surface is equal to zero in the stationary state. This condition is used to perform self-consistent calculations of the grain charge. The spatial distribution of the screened grain potential is studied and compared with the analytical estimates. It is shown that at the distances larger than the Debye length such potential has the Coulomb-like asymptotics with the effective charge dependent on the angle between the radius vector and the external magnetic field direction. The numerical solutions show that in the direction parallel to the external magnetic field the effective potential can have nonmonotonic behavior.

  5. Simultaneous ac and dc magnetic field measurements in residential areas: Implications for resonance theories of biological effects

    SciTech Connect

    Wong, P.S.; Sastre, A.

    1995-10-01

    The goal of this study was to obtain data that could be used to evaluate the applicability of ``resonance`` theories of biological effects in residential settings. The authors first describe a measurement system which allows the study of ac and dc magnetic fields simultaneously in space and in time. Sample measurements were taken near two power lines, two objects and in two residential homes. The results show that the earth`s (dc) magnetic field was unaffected near power lines. The compass orientation of the power line influenced the relative values of the ac components parallel and perpendicular to the dc field. The electric heating system greatly affected the ac field levels in the home, causing the levels to increase from less than 1 mG to a maximum of 7.5 mG during heating. The magnitudes of the dc field in the two homes varied from about 380 to 650 mG, with the larger variations near metallic or magnetic objects such as the refrigerator or a metallic air duct. The earth`s field was elevated above its natural level within a distance of 8 feet from a subcompact passenger car, e.g., the level changed from about 540 to 1,100 mG beside the headlight. A steel chair changed the earth`s field by up to 60 mG within a distance of one foot. These results suggest that some of the narrow ``resonances`` described in laboratory studies may be difficult to observe against the variations in do field amplitude and direction resulting from the presence of everyday metallic objects.

  6. Effects of Magnetic Nanoparticles and External Magnetostatic Field on the Bulk Heterojunction Polymer Solar Cells

    DOE PAGESBeta

    Wang, Kai; Yi, Chao; Liu, Chang; Hu, Xiaowen; Chuang, Steven; Gong, Xiong

    2015-03-18

    The price of energy to separate tightly bound electron-hole pair (or charge-transfer state) and extract freely movable charges from low-mobility materials represents fundamental losses for many low-cost photovoltaic devices. In bulk heterojunction (BHJ) polymer solar cells (PSCs), approximately 50% of the total efficiency lost among all energy loss pathways is due to the photogenerated charge carrier recombination within PSCs and low charge carrier mobility of disordered organic materials. To address these issues, we introduce magnetic nanoparticles (MNPs) and orientate these MNPS within BHJ composite by an external magnetostatic field. Over 50% enhanced efficiency was observed from BHJ PSCs incorporated withmore » MNPs and an external magnetostatic field alignment when compared to the control BHJ PSCs. The optimization of BHJ thin film morphology, suppression of charge carrier recombination, and enhancement in charge carrier collection result in a greatly increased short-circuit current density and fill factor, as a result, enhanced power conversion efficiency.« less

  7. Early detection of colonic dysplasia by magnetic resonance molecular imaging with a contrast agent raised against the colon cancer marker MUC5AC.

    PubMed

    Rossez, Yannick; Burtea, Carmen; Laurent, Sophie; Gosset, Pierre; Léonard, Renaud; Gonzalez, Walter; Ballet, Sébastien; Raynal, Isabelle; Rousseaux, Olivier; Dugué, Timothée; Vander Elst, Luce; Michalski, Jean-Claude; Muller, Robert N; Robbe-Masselot, Catherine

    2016-05-01

    Human gastric mucin MUC5AC is secreted in the colonic mucus of cancer patients and is a specific marker of precancerous lesions called aberrant crypt foci. Using MUC5AC as a specific marker can improve sensitivity in the detection of early colorectal cancer. Here we demonstrated that the accumulation of MUC5AC in xenograft and mouse stomach can be detected by magnetic resonance imaging (MRI). We used ultrasmall particles of iron oxide (USPIOs) conjugated with disulfide constrained heptapeptide that were identified using a screening phage display. To accomplish this, we employed positive selection of the phage display library on MUC5AC purified from fresh human colonic adenomas in combination with negative selection of the phage library on purified human MUC2, which is predominantly found in normal colorectal tissues. This conjugate was tested on human colorectal cancer cell lines that were either able or unable to secrete MUC5AC, both in vitro and in vivo. MUC5AC-USPIO contrast agent and USPIOs alone were not detected in cell lines unable to secrete MUC5AC. A combination of MRI and microscopy studies was performed to detect a specific accumulation of the contrast agent in vivo. Thus, the MUC5AC contrast agent enabled non-invasive detection of precancerous lesions and colorectal cancer, highlighting its potential use in diagnostics, in the early detection of colorectal cancer recurrences after treatment and in mechanistic studies implicating MUC5AC. Copyright © 2016 John Wiley & Sons, Ltd. PMID:26762591

  8. Generation of an external magnetic field with the spin orientation effect in a single layer Ising nanographene

    NASA Astrophysics Data System (ADS)

    Şarlı, Numan

    2016-09-01

    In this work, the magnetic properties of the single layer Ising nanogaphene (SLING) are investigated by using Kaneyoshi approach (KA) within the effective field theory for different spin orientations of its magnetic atoms. We find that the magnetizations of the SLING has no phase transition, certain Curie temperature and distinct peak of susceptibility at Tc for the some spin orientations at the zero external magnetic field (H=0.0). Because these behaviors occur at H≠0.0, we suggest that the SLING generates an external magnetic field and behaves as an external magnetic field generator for these spin orientations. However, the SLING exhibits ferromagnetic behaviors for only one spin orientations. But, it exhibits antiferromagnetic behaviors for the others. For the AFM cases, diamagnetic susceptibility behaviors and type II superconductivity hysteresis behaviors are obtained. We hope that these results can open a door to obtain new class of single layer graphene and graphene-based magnetic field generator devices with the spin orientation effect.

  9. Screening of external magnetic perturbation fields due to sheared plasma flow

    NASA Astrophysics Data System (ADS)

    Li, L.; Liu, Y. Q.; Liang, Y.; Wang, N.; Luan, Q.; Zhong, F. C.; Liu, Y.

    2016-09-01

    Within the single fluid resistive magnetohydrodynamic model, systematic toroidal modelling efforts are devoted to investigate the plasma response induced screening of the applied external 3D magnetic field perturbations in the presence of sheared toroidal flow. One particular issue of interest is addressed, when the local flow speed approaches zero at the perturbation rational surface inside the plasma. Subtle screening physics, associated with the favourable averaged toroidal curvature effect (the GGJ effect (Glasser et al 1975 Phys. Fluids 7 875)), is found to play an essential role during slow flow near the rational surface by enhancing the screening at reduced flow. A strong cancellation effect between different terms of Ohm’s law is discovered, leading to different screening physics in the GGJ regime, as compared to that of conventional screening of the typical resistive-inertial regime occurring at faster flow. These modelling results may be applicable to interpret certain mode locking experiments, as well as type-I edge localized mode suppression experiments, with resonant magnetic field perturbations being applied to tokamak plasmas at low input toroidal torque.

  10. A novel coaxial Ku-band transit radiation oscillator without external guiding magnetic field

    SciTech Connect

    Ling, Junpu Zhang, Jiande; He, Juntao; Jiang, Tao

    2014-02-15

    A novel coaxial transit radiation oscillator without external guiding magnetic field is designed to generate high power microwave at Ku-band. By using a coaxial structure, the space-charge potential energy is suppressed significantly, that is good for enhancing efficient beam-wave interaction. In order to improve the transmission stability of the unmagnetized intense relativistic electron beam, a Pierce-like cathode is employed in the novel device. By contrast with conventional relativistic microwave generators, this kind of device has the advantages of high stability, non-guiding magnetic field, and high efficiency. Moreover, with the coaxial design, it is possible to improve the power-handing capacity by increasing the radial dimension of the Ku-band device. With a 550 keV and 7.5 kA electron beam, a 1.25 GW microwave pulse at 12.08 GHz has been obtained in the simulation. The power conversion efficiency is about 30%.

  11. Effect of external magnetic field on critical current for the onset of virtual cathode oscillations in relativistic electron beams

    NASA Astrophysics Data System (ADS)

    Hramov, Alexander; Koronovskii, Alexey; Morozov, Mikhail; Mushtakov, Alexander

    2008-02-01

    In this Letter we research the space charge limiting current value at which the oscillating virtual cathode is formed in the relativistic electron beam as a function of the external magnetic field guiding the beam electrons. It is shown that the space charge limiting (critical) current decreases with growth of the external magnetic field, and that there is an optimal induction value of the magnetic field at which the critical current for the onset of virtual cathode oscillations in the electron beam is minimum. For the strong external magnetic field the space charge limiting current corresponds to the analytical relation derived under the assumption that the motion of the electron beam is one-dimensional [D.J. Sullivan, J.E. Walsh, E. Coutsias, in: V.L. Granatstein, I. Alexeff (Eds.), Virtual Cathode Oscillator (Vircator) Theory, in: High Power Microwave Sources, vol. 13, Artech House Microwave Library, 1987, Chapter 13]. Such behavior is explained by the characteristic features of the dynamics of electron space charge in the longitudinal and radial directions in the drift space at the different external magnetic fields.

  12. Simultaneous monitoring of singlet and triplet exciton variations in solid organic semiconductors driven by an external static magnetic field

    SciTech Connect

    Ding, Baofu Alameh, Kamal

    2014-07-07

    The research field of organic spintronics has remarkably and rapidly become a promising research area for delivering a range of high-performance devices, such as magnetic-field sensors, spin valves, and magnetically modulated organic light emitting devices (OLEDs). Plenty of microscopic physical and chemical models based on exciton or charge interactions have been proposed to explain organic magneto-optoelectronic phenomena. However, the simultaneous observation of singlet- and triplet-exciton variations in an external magnetic field is still unfeasible, preventing a thorough theoretical description of the spin dynamics in organic semiconductors. Here, we show that we can simultaneously observe variations of singlet excitons and triplet excitons in an external magnetic field, by designing an OLED structure employing a singlet-exciton filtering and detection layer in conjunction with a separate triplet-exciton detection layer. This OLED structure enables the observation of a Lorentzian and a non-Lorentzian line-shape magnetoresponse for singlet excitons and triplet excitons, respectively.

  13. Experiments on plasma immersion ion implantation inside conducting tubes embedded in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Pillaca, E. J. D. M.; Ueda, M.; Reuther, H.; Pichon, L.; Lepienski, C. M.

    2015-12-01

    Tubes of stainless steel (SS) embedded in external magnetic field were used to study the effects of plasma immersion ion implantation (PIII) as a function of their diameter. The study was complemented with and without a grounded auxiliary electrode (AE) placed at the axis of the tube. During the discharge tests in tubes of larger diameter (D = 11 cm), with and without AE, nitrogen gas breakdown was established inside the tube at pressures near 2.0 × 10-2 mbar. Under the same operation conditions, stable plasmas with similar PIII current densities were obtained for both arrangements. Reducing the diameter of the tube (D = 1.5 cm) turned the plasma unstable and made it inappropriate for ion implantation. This situation was solved by supplying gas at higher pressure or using higher magnetic field, without the presence of an AE. Under these conditions, nitrogen PIII treatments of these small diameter tubes were performed but gave not the best implantation results yet. Our results have also shown higher ion implantation current density (16 mA/cm2) in tube of intermediate diameter (D = 4 cm) using AE, compared to largest diameter tube used. In this case, a thick nitrogen layer of about 9 μm was obtained in the SS sample placed inside the tube. As a consequence of this, its structural and mechanical properties were enhanced. These results are attributed to the thermal diffusion promoted by ions hitting the inner wall in a large number due to the presence of the AE and the magnetic field.

  14. AC driven magnetic domain quantification with 5 nm resolution

    PubMed Central

    Li, Zhenghua; Li, Xiang; Dong, Dapeng; Liu, Dongping; Saito, H.; Ishio, S.

    2014-01-01

    As the magnetic storage density increases in commercial products, e.g. the hard disc drives, a full understanding of dynamic magnetism in nanometer resolution underpins the development of next-generation products. Magnetic force microscopy (MFM) is well suited to exploring ferromagnetic domain structures. However, atomic resolution cannot be achieved because data acquisition involves the sensing of long-range magnetostatic forces between tip and sample. Moreover, the dynamic magnetism cannot be characterized because MFM is only sensitive to the static magnetic fields. Here, we develop a side-band magnetic force microscopy (MFM) to locally observe the alternating magnetic fields in nanometer length scales at an operating distance of 1 nm. Variations in alternating magnetic fields and their relating time-variable magnetic domain reversals have been demonstrated by the side-band MFM. The magnetic domain wall motions, relating to the periodical rotation of sample magnetization, are quantified via micromagnetics. Based on the side-band MFM, the magnetic moment can be determined locally in a volume as small as 5 nanometers. The present technique can be applied to investigate the microscopic magnetic domain structures in a variety of magnetic materials, and allows a wide range of future applications, for example, in data storage and biomedicine. PMID:25011670

  15. Ground state energy of an exciton in a spherical quantum dot in the presence of an external magnetic field

    SciTech Connect

    Jahan K, Luhluh Boda, Aalu; Chatterjee, Ashok

    2015-05-15

    The problem of an exciton trapped in a three dimensional Gaussian quantum dot is studied in the presence of an external magnetic field. A variational method is employed to obtain the ground state energy of the exciton as a function of the quantum dot size, the confinement strength and the magnetic field. It is also shown that the variation of the size of the exciton with the radius of the quantum dot.

  16. Analysis of the influence of external magnetic field on transition matrix elements in quantum well and quantum cascade laser structures

    NASA Astrophysics Data System (ADS)

    Demić, Aleksandar; Radovanović, Jelena; Milanović, Vitomir

    2016-08-01

    We present a method for modeling nonparabolicity effects (NPE) in quantum nanostructures in presence of external electric and magnetic field by using second order perturbation theory. The method is applied to analysis of quantum well structure and active region of a quantum cascade laser (QCL). This model will allow us to examine the influence of magnetic field on dipole matrix element in QCL structures, which will provide a better insight to how NPE can affect the gain of QCL structures.

  17. Tools and Setups for Experiments with AC and Rotating Magnetic Fields

    ERIC Educational Resources Information Center

    Ponikvar, D.

    2010-01-01

    A rotating magnetic field is the basis for the transformation of electrical energy to mechanical energy. School experiments on the rotating magnetic field are rare since they require the use of specially prepared mechanical setups and/or relatively large, three-phase power supplies to achieve strong magnetic fields. This paper proposes several…

  18. Influence of externally applied magnetic perturbations on neoclassical tearing modes at ASDEX Upgrade

    NASA Astrophysics Data System (ADS)

    Fietz, S.; Bergmann, A.; Classen, I.; Maraschek, M.; Garcia-Muñoz, M.; Suttrop, W.; Zohm, H.; the ASDEX Upgrade Team

    2015-01-01

    The influence of externally applied magnetic perturbations (MPs) on neoclassical tearing modes (NTM) and the plasma rotation in general is investigated at the ASDEX Upgrade tokamak (AUG). The low n resonant components of the applied field exert local torques and influence the stability of NTMs. The non-resonant components of the error field do not influence MHD modes directly but slow down the plasma rotation globally due to a neoclassical toroidal viscous torque (NTV). Both components slow down the plasma rotation, which in consequence increases the probability for the appearance of locked modes. To investigate the impact of externally applied MPs on already existing modes and the influence on the rotation profile, experimental observations are compared to modelling results. The model used here solves a coupled equation system that includes the Rutherford equation and the equation of motion, taking into account the resonant effects and the resistive wall. It is shown that the NTV torque can be neglected in this modelling. To match the experimental frequency evolution of the mode the MP field strength at the resonant surface has to be increased compared to the vacuum approximation. This leads to an overestimation of the stabilizing effect on the NTMs. The reconstruction of the entire rotation profile via the equation of motion including radial dependencies, confirms that the NTV is negligibly small and that small resonant torques at different resonant surfaces have the same effect as one large one. This modelling suggests that in the experiment resonant torques at different surfaces are acting and slowing down the plasma rotation requiring a smaller torque at the specific resonant surface of the NTM. This additionally removes the overestimated influence on the island stability, whereas the braking of the island's rotation is caused by the sum of all torques. Consequently, to describe the effect of MPs on the evolution of one island, all other islands and the

  19. Physical and Mechanical Characterization of Electrodeposited Nickel Nanowires -- Influence of Current Density and External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Samykano, Mahendran

    Magnetic 1-D nanostructures have received great interest due to their various applications including high-density magnetic storage, sensors, drug delivery, and NEMS/MEMS systems. Among different 1-D nanostructures, magnetic nickel (Ni) nanowires with their ferromagnetic properties are of interest in such applications due to their lower cost, and they can be consistently synthesized via electrodeposition. While physical properties are influenced by processing parameters during electrodeposition of Ni nanowires, understanding of their influence on the mechanical properties is still not available. This is primarily due to the following challenges: tediousness involved in experimental techniques for mechanical characterization at nanoscale; sophisticated and careful experimentation required to be performed with advanced microscopy systems (SEM, AFM); robust nanoscale manipulators needed to place a single nanowire within the device; and difficulty in correctly loading and obtaining data for stress-strain within high powered microscopy environments. All of these factors pose significant challenges, limiting the current state of the art in mechanical characterization to its infancy, with wide differences in characterization curves and reported properties in this field. The present research and dissertation focuses on: 1. Experimental synthesis of electrodeposited Ni nanowires at different current densities and external magnetic fields, 2. Physical properties characterization of the synthesized nanowires to understand their morphology, structural and crystallographic properties, 3. Mechanical properties characterization of synthesized Ni nanowires through careful experiments within scanning electron microscope (SEM) based on uni-axial MEMS tensile loading device, 4. Data analysis to understand the process, physical and mechanical property interrelationship and to obtain insights on tensile deformation and failure modes observed in the Ni nanowires studied. Key research

  20. Effective method to measure back emfs and their harmonics of permanent magnet ac motors

    NASA Astrophysics Data System (ADS)

    Jiang, Q.; Bi, C.; Lin, S.

    2006-04-01

    As the HDD spindle motors become smaller and smaller, the back electromotive forces (emfs) measurement faces the new challenges due to their low inertias and small sizes. This article proposes a novel method to measure the back emfs and their harmonic components of PM ac motors only through a freewheeling procedure. To eliminate the influence of the freewheeling deceleration, the phase flux linkages are employed to obtain the back emf amplitudes and phases of the fundamental and harmonic components by using finite Fourier series analysis. The proposed method makes the freewheeling measurement of the back emfs and their harmonics accurate and fast. It is especially useful for the low inertia PM ac motors, such as spindle motors for small form factor HDDs.

  1. Introduction and pinning of domain walls in 50 nm NiFe constrictions using local and external magnetic fields

    NASA Astrophysics Data System (ADS)

    Zahnd, G.; Pham, V. T.; Marty, A.; Jamet, M.; Beigné, C.; Notin, L.; Vergnaud, C.; Rortais, F.; Vila, L.; Attané, J.-P.

    2016-05-01

    We study domain wall injection in 100 nm wide NiFe nanowires, followed by domain wall propagation and pinning on 50 nm wide constrictions. The injection is performed using local and external magnetic fields. Using several nucleation pad geometries, we show that at these small dimensions the use of an external field only does not allow obtaining a reproducible injection/pinning process. However, the use of an additional local field, created by an Oersted line, allows to nucleate a reversed domain at zero external applied field. Then, an external field of 5 mT enables the domain wall to propagate far from the Oersted line, and the pinning occurs reproducibly. We also show that notwithstanding the reproducibility of the pinning process, the depinning field is found to be stochastic, following a bimodal distribution. Using micromagnetic simulation we link two different DW configurations, vortex and transverse, to the two typical depinning fields.

  2. Rotational Brownian dynamics simulations of non-interacting magnetized ellipsoidal particles in d.c. and a.c. magnetic fields

    NASA Astrophysics Data System (ADS)

    Sánchez, Jorge H.; Rinaldi, Carlos

    2009-10-01

    The rotational Brownian motion of magnetized tri-axial ellipsoidal particles (orthotropic particles) suspended in a Newtonian fluid, in the dilute suspension limit, under applied d.c. and a.c. magnetic fields was studied using rotational Brownian dynamics simulations. The algorithm describing the change in the suspension magnetization was obtained from the stochastic angular momentum equation using the fluctuation-dissipation theorem and a quaternion formulation of orientation space. Simulation results are in agreement with the Langevin function for equilibrium magnetization and with single-exponential relaxation from equilibrium at small fields using Perrin's effective relaxation time. Dynamic susceptibilities for ellipsoidal particles of different aspect ratios were obtained from the response to oscillating magnetic fields of different frequencies and described by Debye's model for the complex susceptibility using Perrin's effective relaxation time. Simulations at high equilibrium and probe fields indicate that Perrin's effective relaxation time continues to describe relaxation from equilibrium and response to oscillating fields even beyond the small field limit.

  3. The 1-loop self-energy of an electron in a strong external magnetic field revisited

    NASA Astrophysics Data System (ADS)

    Machet, B.

    2016-05-01

    I calculate the 1-loop self-energy of the lowest Landau level of an electron of mass m in a strong, constant and uniform external magnetic field B, beyond its always used truncation at (ln L)2, L = |e|B m2. This is achieved by evaluating the integral deduced in 1953 by Demeur and incompletely calculated in 1969 by Jancovici, which I recover from Schwinger’s techniques of calculation. It yields δm ≃ αm 4π ln L ‑ γE ‑3 22 ‑9 4 + π β‑1 + π2 6 + πΓ[1‑β] Lβ‑1 + 1 L π 2‑β ‑ 5 + 𝒪 1 L≥2 with β ≃ 1.175 for 75 ≤ L ≤ 10, 000. The (ln L)2 truncation exceeds the precise estimate by 45% at L = 100 and by more at lower values of L, due to neglecting, among others, the single logarithmic contribution. This is doubly unjustified because it is large and because it is needed to fulfill appropriate renormalization conditions. Technically challenging improvements look therefore necessary, for example, when resumming higher loops and incorporating the effects of large B on the photonic vacuum polarization, like investigated in recent years.

  4. Giant frequency tunability enabled by external magnetic and a gate electric fields in graphene devices.

    PubMed

    Hu, Xiang; Huang, Qiuping; Zhao, Yi; Cai, Honglei; Knize, Randy J; Lu, Yalin

    2016-03-21

    Graphene possesses a unique Landau level system that is non-equidistantly spaced in energy, as thus a large amount of optical transitions may become possible. Here, by utilizing this unique feature, we propose a novel dual field method which combines both external magnetic field and gate electric field together to control the optical response of the graphene-based devices. The key principle of this method is to selectively allow different optical transitions in graphene among Landau levels via an electric gate tuning of the Fermi level. By applying this method to a graphene based amplitude modulator and through an implementation based on transfer matrix method, we numerically demonstrated the well characteristics of switchable modulation on four individual channels, a huge modulation depth up to 80 dB and an extremely low required energy of tuning Fermi level down to 10 meV. Such excellent frequency tunability and gate controlling ability of this dual field method may open up the potential for applications in active optoelectronics, spin optics, ultrafast optics and etc. PMID:27136850

  5. Trajectory control of PbSe–γ-Fe2O3 nanoplatforms under viscous flow and an external magnetic field

    PubMed Central

    Etgar, Lioz; Nakhmani, Arie; Tannenbaum, Allen; Lifshitz, Efrat; Tannenbaum, Rina

    2010-01-01

    The flow behavior of nanostructure clusters, consisting of chemically bonded PbSe quantum dots and magnetic γ -Fe2O3 nanoparticles, has been investigated. The clusters are regarded as model nanoplatforms with multiple functionalities, where the γ -Fe2O3 magnets serve as transport vehicles, manipulated by an external magnetic field gradient, and the quantum dots act as fluorescence tags within an optical window in the near-infrared regime. The clusters’ flow was characterized by visualizing their trajectories within a viscous fluid (mimicking a blood stream), using an optical imaging method, while the trajectory pictures were analyzed by a specially developed processing package. The trajectories were examined under various flow rates, viscosities and applied magnetic field strengths. The results revealed a control of the trajectories even at low magnetic fields (<1 T), validating the use of similar nanoplatforms as active targeting constituents in personalized medicine. PMID:20368678

  6. A Comparison of Methods to Measure the Magnetic Moment of Magnetotactic Bacteria through Analysis of Their Trajectories in External Magnetic Fields

    PubMed Central

    Fradin, Cécile

    2013-01-01

    Magnetotactic bacteria possess organelles called magnetosomes that confer a magnetic moment on the cells, resulting in their partial alignment with external magnetic fields. Here we show that analysis of the trajectories of cells exposed to an external magnetic field can be used to measure the average magnetic dipole moment of a cell population in at least five different ways. We apply this analysis to movies of Magnetospirillum magneticum AMB-1 cells, and compare the values of the magnetic moment obtained in this way to that obtained by direct measurements of magnetosome dimension from electron micrographs. We find that methods relying on the viscous relaxation of the cell orientation give results comparable to that obtained by magnetosome measurements, whereas methods relying on statistical mechanics assumptions give systematically lower values of the magnetic moment. Since the observed distribution of magnetic moments in the population is not sufficient to explain this discrepancy, our results suggest that non-thermal random noise is present in the system, implying that a magnetotactic bacterial population should not be considered as similar to a paramagnetic material. PMID:24349185

  7. Roles of Atomic Injection Rate and External Magnetic Field on Optical Properties of Elliptical Polarized Probe Light

    NASA Astrophysics Data System (ADS)

    Karimi, R.; Asadpour, S. H.; Batebi, S.; Rahimpour Soleimani, H.

    2016-01-01

    In this paper we investigate the optical properties of an open four-level tripod atomic system driven by an elliptically polarized probe field in the presence of the external magnetic field and compare its properties with the corresponding closed system. Our result reveals that absorption, dispersion and group velocity of probe field can be manipulated by adjusting the phase difference between the two circularly polarized components of a single coherent field, magnetic field and cavity parameters i.e. the atomic exit rate from cavity and atomic injection rates. We show that the system can exhibit multiple electromagnetically induced transparency windows in the presence of the external magnetic field. The numerical result shows that the probe field in the open system can be amplified by appropriate choice of cavity parameters, while in the closed system with introduce appropriate phase difference between fields the probe field can be enhanced. Also it is shown that the group velocity of light pulse can be controlled by external magnetic field, relative phase of applied fields and cavity parameters. By changing the parameters the group velocity of light pulse changes from subluminal to superluminal light propagation and vice versa.

  8. Nonlinear and ac Susceptibility of the Dilute Ising Magnet LiHoxY1-xF4

    NASA Astrophysics Data System (ADS)

    Quilliam, Jeffrey; Meng, Shuchao; Mugford, Chas; Kycia, Jan

    2008-03-01

    Recent work has called into question the existence of a spin glass transition in the dilute dipolar Ising magnet LiHoxY1-xF4 [1]. Other work has suggested that there is an exotic spin liquid phase found at a Ho concentration of x = 0.045 [2]. In order to carefully study the dynamics of this system, we have put together a SQUID magnetometer which allows for measurements of ac susceptibility and nonlinear susceptibility over a large frequency range. We present results from measurements on single crystals of LiHoxY1-xF4, particularly on an x = 0.045 sample, in an attempt to either reproduce the exotic ``anti-glass'' physics that was previously observed or to detect a spin glass transition. [1] P. E. Jonnson et al. PRL 98, 256403 (2007) [2] S. Ghosh et al. Science 296, 2195 (2002)

  9. Linearity of the Faraday-rotation-type ac magnetic-field sensor with a ferrimagnetic or ferromagnetic rotator film

    NASA Astrophysics Data System (ADS)

    Mori, Hiroshi; Asahara, Yousuke

    1996-03-01

    We analyze the linearity and modulation depth of ac magnetic-field sensors or current sensors, using a ferrimagnetic or ferromagnetic film as the Faraday rotator and employing the detection of only the zeroth-order optical diffraction component from the rotator. It is theoretically shown that for this class of sensor the condition of a constant modulation depth and that of a constant ratio error give an identical series of curves for the relationship between Faraday rotation angle greater than or equals V and polarizer/analyzer relative angle Phi . We give some numerical examples to demonstrate the usefulness of the result with reference to a rare-earth iron garnet film as the rotator.

  10. Monitoring of changes in cluster structures in water under AC magnetic field

    NASA Astrophysics Data System (ADS)

    Usanov, A. D.; Ulyanov, S. S.; Ilyukhina, N. S.; Usanov, D. A.

    2016-01-01

    A fundamental possibility of visualizing cluster structures formed in distilled water by an optical method based on the analysis of dynamic speckle structures is demonstrated. It is shown for the first time that, in contrast to the existing concepts, water clusters can be rather large (up to 200 -m in size), and their lifetime is several tens of seconds. These clusters are found to have an internal spatially inhomogeneous structure, constantly changing in time. The properties of magnetized and non-magnetized water are found to differ significantly. In particular, the number of clusters formed in magnetized water is several times larger than that formed in the same volume of non-magnetized water.

  11. Continuous Paranematic Ordering of Rigid and Semiflexible Amyloid-Fe3O4 Hybrid Fibrils in an External Magnetic Field.

    PubMed

    Zhao, Jianguo; Bolisetty, Sreenath; Isabettini, Stéphane; Kohlbrecher, Joachim; Adamcik, Jozef; Fischer, Peter; Mezzenga, Raffaele

    2016-08-01

    External magnetic field is a powerful approach to induce orientational order in originally disordered suspensions of magneto-responsive anisotropic particles. By small angle neutron scattering and optical birefringence measurement technology, we investigated the effect of magnetic field on the spatial ordering of hybrid amyloid fibrils with different aspect ratios (length-to-diameter) and flexibilities decorated by spherical Fe3O4 nanoparticles. A continuous paranematic ordering from an initially isotropic suspension was observed upon increasing magnetic field strength, with spatial orientation increasing with colloidal volume fraction. At constant dimensionless concentration, stiff hybrid fibrils with varying aspect ratios and volume fractions, fall on the same master curve, with equivalent degrees of ordering at identical magnetic fields. However, the semiflexible hybrid fibrils with contour length close to persistence length exhibit a lower degree of alignment. This is consistent with Khokhlov-Semenov theoretical predictions. These findings sharpen the experimental toolbox to design colloidal systems with controllable degree of orientational ordering. PMID:27304090

  12. The mechanical properties of high speed GTAW weld and factors of nonlinear multiple regression model under external transverse magnetic field

    NASA Astrophysics Data System (ADS)

    Lu, Lin; Chang, Yunlong; Li, Yingmin; He, Youyou

    2013-05-01

    A transverse magnetic field was introduced to the arc plasma in the process of welding stainless steel tubes by high-speed Tungsten Inert Gas Arc Welding (TIG for short) without filler wire. The influence of external magnetic field on welding quality was investigated. 9 sets of parameters were designed by the means of orthogonal experiment. The welding joint tensile strength and form factor of weld were regarded as the main standards of welding quality. A binary quadratic nonlinear regression equation was established with the conditions of magnetic induction and flow rate of Ar gas. The residual standard deviation was calculated to adjust the accuracy of regression model. The results showed that, the regression model was correct and effective in calculating the tensile strength and aspect ratio of weld. Two 3D regression models were designed respectively, and then the impact law of magnetic induction on welding quality was researched.

  13. Compact electromagnetically operated microfluidic system for detection of sub-200-nm magnetic labels for biosensing without external pumps

    NASA Astrophysics Data System (ADS)

    Morimoto, Y.; Takamura, T.; Sandhu, A.

    2010-05-01

    The combination of small sample analyte volumes, high sensitivity, ease of use, high speed, and portability is an important factor for the development of protocols for point of care biodiagnosis. Currently, handling small amounts of liquids is achieved using microfluidic systems but it is challenging to satisfy the remaining factors using conventional approaches based on biosensors employing detection of fluorescent labels. Thus to resolve the other requirements, biosensing systems based on the detection of functionalized superparamagnetic beads acting as "magnetic labels" are being studied as an alternative approach. Notably, for greater quantification, there are increasing demands for the use of sub-200-nm magnetic labels, which are comparable in size to actual biomolecules. However, detection of small numbers of sub-200-nm diameter magnetic beads by magnetoresistive device-based platforms is extremely challenging due to the intrinsic noise of the electronic devices. In order to overcome the limitation, we have developed a simple procedure for detecting sub-200-nm diameter magnetic labels for biosensing via magnetically induced self-assembly of superparamagnetic beads. Applying our approach to conventional microfluidic systems satisfies the most of prerequisites; however conventional microfluidic systems attached to the external pumps are yet suitable for point of care biodiagnosis. Here we propose the development of an alternative biosensing system based on our previous work that does not require external pumps to achieve miniaturization.

  14. Current-voltage characteristics of hydrogen DC plasma torches with different sizes in an external axial magnetic field

    NASA Astrophysics Data System (ADS)

    Ma, Jie; Wen, Guang-Dong; Su, Bao-Gen; Yang, Yi-Wen; Ren, Qi-Long

    2015-06-01

    Current-voltage (I-V) characteristics of hydrogen DC plasma torches with different sizes in an external axial magnetic field under atmospheric pressure are reported. Three anodes with different diameters are adopted in a 50-kW torch: 25 mm, 30 mm, and 35 mm, respectively. Two different diameters of anodes, that is, 100 mm and 130 mm, are adopted in a 1-MW plasma torch. The arc voltage shows a negative trend with the increase of arc current under the operating regimes. On the contrary, arc voltage shows a positive trend as the flow rate of carrier gas increases, and a similar trend is found with increasing the external magnetic flux density. A similarity formula is constructed to correlate the experimental data of the torches mentioned above. Linear fitting shows that the Pearson correlation coefficient is 0.9958. Project supported by the Special Fund for Basic Scientific Research of Central Colleges, China (Grant No. 2012FZA4023).

  15. Review of russian literature on biological action of DC and low-frequency AC magnetic fields.

    PubMed

    Zhadin, M N

    2001-01-01

    This review considers the Russian scientific literature on the influence of weak static and of low-frequency alternating magnetic fields on biological systems. The review covers the most interesting works and the main lines of investigation during the period 1900 to the present. Shown here are the historical roots, beginning with the ideas of V. Vernadsky and A. Chizhevsky, which led in the field of Russian biology to an increasing interest in magnetic fields, based on an intimate connection between solar activity and life on the Earth, and which determined the peculiar development of Russian magnetobiology. The variety of studies on the effects of magnetic storms and extremely low-frequency, periodic variations of the geomagnetic field on human beings and animals as well as on social phenomena are described. The diverse experiments involving artificial laboratory magnetic fields acting on different biological entities under different conditions are also considered. A series of theoretical advances are reviewed that have paved the way for a step-by-step understanding of the mechanisms of magnetic field effects on biological systems. The predominantly unfavorable influence of magnetic fields on living beings is shown, but the cases of favorable influence of magnetic fields on human beings and lower animals are demonstrated as well. The majority of Russian investigations in this area of science has been unknown among the non-Russian speaking audience for many reasons, primarily because of a language barrier. Therefore, it is hoped that this review may be of interest to the international scientific community. PMID:11122491

  16. Study of AC Magnetic Properties and Core Losses of Fe/Fe3O4-epoxy Resin Soft Magnetic Composite

    NASA Astrophysics Data System (ADS)

    Laxminarayana, T. A.; Manna, Subhendu Kumar; Fernandes, B. G.; Venkataramani, N.

    Soft Magnetic Composites (SMC) were prepared by coating of nanocrystalline Fe3O4 particles, synthesized by co-precipitation method, on atomized iron powder of particle size less than 53 μm in size using epoxy resin as a binder between iron and Fe3O4. Fe3O4 was chosen, for its high electric resistivity and suitable magnetic properties, to keep the coating layer magnetic and seek improvement to the magnetic properties of SMC. SEM images and XRD patterns were recorded in order to investigate the coatings on the surface of iron powder. A toroid was prepared by cold compaction of coated iron powder at 1050 MPa and subsequently cured at 150˚C for 1 hr in argon atmosphere. For comparison of properties, a toroid of uncoated iron powder was also compacted at 1050 MPa and annealed at 600˚C for 2 hr in argon atmosphere. The coated iron powder composite has a resistivity of greater than 200 μΩm, measured by four probe method. A comparison of Magnetic Hysteresis loops and core losses using B-H Loop tracer in the frequency range 0 to 1500 Hz on the coated and uncoated iron powder is reported.

  17. AC loss in superconducting tapes and cables

    NASA Astrophysics Data System (ADS)

    Oomen, Marijn Pieter

    High-temperature superconductors are developed for use in power-transmission cables, transformers and motors. The alternating magnetic field in these devices causes AC loss, which is a critical factor in the design. The study focuses on multi-filament Bi-2223/Ag tapes exposed to a 50-Hz magnetic field at 77 K. The AC loss is measured with magnetic, electric and calorimetric methods. The results are compared to theoretical predictions based mainly on the Critical-State Model. The loss in high- temperature superconductors is affected by their characteristic properties: increased flux creep, high aspect ratio and inhomogeneties. Filament intergrowths and a low matrix resistivity cause a high coupling-current loss especially when the filaments are fully coupled. When the wide side of the tape is parallel to the external magnetic field, the filaments are decoupled by twisting. In a perpendicular field the filaments can be decoupled only by combining a short twist pitch with a transverse resistivity much higher than that of silver. The arrangement of the inner filaments determines the transverse resistivity. Ceramic barriers around the filaments cause partial decoupling in perpendicular magnetic fields at power frequencies. The resultant decrease in AC loss is greater than the accompanying decrease in critical current. With direct transport current in alternating magnetic field, the transport-current loss is well described with a new model for the dynamic resistance. The Critical- State Model describes well the magnetisation and total AC loss in parallel magnetic fields, at transport currents up to 0.7 times the critical current. When tapes are stacked face-to-face in a winding, the AC-loss density in perpendicular fields is greatly decreased due to the mutual shielding of the tapes. Coupling currents between the tapes in a cable cause an extra AC loss, which is reduced by a careful cable design. The total AC loss in complex devices with many tapes is generally well

  18. A cluster-glass magnetic state in R5Pd2 (R = Ho, Tb) compounds evidenced by AC-susceptibility and neutron scattering measurements.

    PubMed

    Gubkin, A F; Sherstobitova, E A; Terentyev, P B; Hoser, A; Baranov, N V

    2013-06-12

    AC- and DC-susceptibility, high-field magnetization and neutron diffraction measurements have been performed in order to study the magnetic state of R5Pd2 (R = Ho, Tb) compounds. The results show that both compounds undergo cluster-glass freezing upon cooling below Tf. According to the neutron diffraction a long-range magnetic order is absent down to 2 K and magnetic clusters with short-range incommensurate antiferromagnetic correlations exist not only below Tf but also in a wide temperature range above the freezing temperature (at least up to 2Tf). A complex cluster-glass magnetic state existing in Ho5Pd2 and Tb5Pd2 down to low temperatures results in rather complicated magnetization behavior in DC and AC magnetic fields. Such an unusual magnetic state in compounds with a high rare-earth concentration may be associated with the layered type of their crystal structure and with substantial atomic disorder, which results in frustrations in the magnetic subsystem. PMID:23676314

  19. On the temperature dependence of the ac susceptibility of Fe 3O 4 magnetic fluids

    NASA Astrophysics Data System (ADS)

    Abu-Aljarayesh, I.; Al-Rawi, A.; Abu-Safia, H.

    1993-02-01

    The temperature dependence of the frequency-dependent magnetic susceptibility has been measured for Fe 3O 4 magnetic fluids with Isopar-M as a liquid carrier. The temperature range was 80 K ≤ T ≤ 300 K, and the volume fractions ɛ ranged from 0.004 to 0.062. With increasing temperature the in-phase magnetic susceptibility χ' increased from its initial value to a maximum at a temperature TB, then decreased monotonically until around the melting point of the liquid carrier, Tm ≈ 200 K. For T ≤ Tm, χ' increased rapidly to a second maximum at T = TB1. This behaviour was qualitatively similar for all studied samples. For the sample with ɛ = 0.047, χ' decreased with increasing frequency at all temperatures. When a static magnetic field was applied, a reduction in χ' was also observed. The effects of interparticle interactions on the static initial susceptibility χ i, are discussed. Analysis of the data yields information about the effective anisotropy energy, the median magnetic diameter, and relaxation times. The distribution of blocking temperature was calculated from the superparamagnetic blocking model of Wohlfarth. The results are further analysed and discussed within the framework of Lundgren model of spin glasses.

  20. Attenuation of Mouse Melanoma by A/C Magnetic Field after Delivery of Bi-Magnetic Nanoparticles by Neural Progenitor Cells

    PubMed Central

    Rachakatla, Raja Shekar; Balivada, Sivasai; Seo, Gwi-Moon; Myers, Carl B; Wang, Hongwang; Samarakoon, Thilani N.; Dani, Raj; Pyle, Marla; Kroh, Franklin O.; Walker, Brandon; Leaym, Xiaoxuan; Koper, Olga B.; Chikan, Viktor; Bossmann, Stefan H.; Tamura, Masaaki; Troyer, Deryl L.

    2010-01-01

    Localized magnetic hyperthermia as a treatment modality for cancer has generated renewed interest, particularly if it can be targeted to the tumor site. We examined whether tumor-tropic neural progenitor cells (NPCs) could be utilized as cell delivery vehicles for achieving preferential accumulation of core/shell iron/iron oxide magnetic nanoparticles (MNPs) within a mouse model of melanoma. We developed aminosiloxane-porphyrin functionalized MNPs, evaluated cell viability and loading efficiency, and transplanted neural progenitor cells loaded with this cargo into mice with melanoma. NPCs were efficiently loaded with core/shell Fe/Fe3O4 MNPs with minimal cytotoxicity; the MNPs accumulated as aggregates in the cytosol. The NPCs loaded with MNPs could travel to subcutaneous melanomas, and after A/C (alternating current) magnetic field (AMF) exposure, the targeted delivery of MNPs by the cells resulted in a measurable regression of the tumors. The tumor attenuation was significant (p<0.05) a short time (24 hours) after the last of three AMF exposures. PMID:21058696

  1. Compression and Cavitation of Externally Applied Magnetic Field on a Hohlraum due to Non-Local Heat Flow Effects

    NASA Astrophysics Data System (ADS)

    Joglekar, Archis; Thomas, Alec; Ridgers, Chris; Kingham, Rob

    2015-11-01

    In this study, we present full-scale 2D kinetic modeling of externally imposed magnetic fields on hohlraums with laser heating. We observe magnetic field cavitation and compression due to thermal energy transport. Self-consistent modeling of the electron momentum equation allows for a complete treatment of the heat flow equation and Ohm's Law. A complete Ohm's Law contains magnetic field advection through the Nernst mechanism that arises due to the heat flow. Magnetic field amplification by a factor of 3 occurs due to magnetic flux pile-up from Nernst convection. The magnetic field cavitates towards the hohlraum axis over a 0.5 ns time scale due to Nernst convection. This results in significantly different magnetic field profiles and slower cavitation than can be expected due to the plasma bulk flow. Non-local electrons contribute to the heat flow down the density gradient resulting in an augmented Nernst convection mechanism that is included self-consistently through kinetic modeling. In addition to showing the prevalence of non-local heat flows, we show effects such as anomalous heat flow up the density gradient induced by inverse bremsstrahlung heating. This research was supported by the DOE through Grant No. DE SC0010621 and in part through computational resources and services provided by Advanced Research Computing at the University of Michigan, Ann Arbor.

  2. Applied AC and DC magnetic fields cause alterations in the mitotic cycle of early sea urchin embryos

    SciTech Connect

    Levin, M.; Ernst, S.G.

    1995-09-01

    This study demonstrates that exposure to 60 Hz magnetic fields (3.4--8.8 mt) and magnetic fields over the range DC-600 kHz (2.5--6.5 mT) can alter the early embryonic development of sea urchin embryos by inducing alterations in the timing of the cell cycle. Batches of fertilized eggs were exposed to the fields produced by a coil system. Samples of the continuous cultures were taken and scored for cell division. The times of both the first and second cell divisions were advanced by ELF AC fields and by static fields. The magnitude of the 60 Hz effect appears proportional to the field strength over the range tested. the relationship to field frequency was nonlinear and complex. For certain frequencies above the ELF range, the exposure resulted in a delay of the onset of mitosis. The advance of mitosis was also dependent on the duration of exposure and on the timing of exposure relative to fertilization.

  3. Dual AC Dipole Excitation for the Measurement of Magnetic Multipole Strength from Beam Position Monitor Data

    SciTech Connect

    M. Spata, G.A. Krafft

    2011-09-01

    An experiment was conducted at Jefferson Lab's Continuous Electron Beam Accelerator Facility to develop a technique for characterizing the nonlinear fields of the beam transport system. Two air-core dipole magnets were simultaneously driven at two different frequencies to provide a time-dependent transverse modulation of the electron beam. Fourier decomposition of beam position monitor data was then used to measure the amplitude of these frequencies at different positions along the beamline. For a purely linear transport system one expects to find solely the frequencies that were applied to the dipoles with amplitudes that depend on the phase advance of the lattice. In the presence of nonlinear fields one expects to also find harmonics of the driving frequencies that depend on the order of the nonlinearity. The technique was calibrated using one of the sextupole magnets in a CEBAF beamline and then applied to a dipole to measure the sextupole and octupole strength of the magnet. A comparison is made between the beam-based measurements, results from TOSCA and data from our Magnet Measurement Facility.

  4. Numerical simulation of high-current vacuum arc characteristics under combined action of axial magnetic field and external magnetic field from bus bar

    SciTech Connect

    Wang Lijun; Jia Shenli; Liu Ke; Wang Liuhuo; Shi Zongqian

    2009-10-15

    In this paper, the two-dimensional high-current vacuum arc (HCVA) model under the combined action of axial magnetic field (AMF) and external magnetic field from bus bar (EMFBB) is established. Based on this model, the influence of AMF and EMFBB on HCVA characteristics can be simulated and analyzed. Simulation results show that the HCVA column will be deflected by the Lorentz force generated by EMFBB and higher arc current. Moreover, the deflection level will be increased with the increase in external EMFBB strength. For HCVA, due to the smaller axial velocity near cathode side, the deflection of plasma parameters (such as ion number density, ion temperature, electron temperature, plasma pressure, and so on) near cathode side is more significant than that near anode side. The current deflection near cathode side toward direction of Lorentz force is more significant than that near anode side.

  5. Sinusoïdal flow of blood in a cylindrical deformable vessel exposed to an external magnetic field

    NASA Astrophysics Data System (ADS)

    Drochon, Agnès

    2016-03-01

    The present work provides an analytical solution for the Sinusoïdal flow of blood in a cylindrical elastic vessel exposed to an external magnetic field. The vessel is supposed to have non-conducting walls and the induced electric and magnetic fields are neglected. In other words, the well-known calculation of Womersley is revisited through the inclusion of the Lorentz force in the Navier-Stokes equations. A dispersion equation is obtained. This equation admits two types of solutions: the Young waves (mainly associated with radial deformation of the vessel) and the Lamb waves (mainly associated with longitudinal displacements in the vessel wall). It is demonstrated that the external magnetic field has an influence on the wave celerities, on the fluid velocity profiles, and on the wall displacements. It tends to reduce the blood flow and flatten the velocity profile, in the case of Young waves. The pulsatile character of the flow is also dampened. However, these effects become detectable for high values of the Hartmann number (M > 4, corresponding to B0 > 36 T with numerical data pertaining to large human arteries) and remain negligible in the context of magnetic resonance imaging (B0 ≤ 3 T, or even 7 T).

  6. Investigation of the chaotic dynamics of an electron beam with a virtual cathode in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Egorov, E. N.; Hramov, A. E.

    2006-08-01

    The effect of the strength of the focusing magnetic field on chaotic dynamic processes occurring in an electron beam with a virtual cathode, as well as on the processes whereby the structures form in the beam and interact with each other, is studied by means of two-dimensional numerical simulations based on solving a self-consistent set of Vlasov-Maxwell equations. It is shown that, as the focusing magnetic field is decreased, the dynamics of an electron beam with a virtual cathode becomes more complicated due to the formation and interaction of spatiotemporal longitudinal and transverse structures in the interaction region of a vircator. The optimum efficiency of the interaction of an electron beam with the electromagnetic field of the vircator is achieved at a comparatively weak external magnetic field and is determined by the fundamentally two-dimensional nature of the motion of the beam electrons near the virtual cathode.

  7. Simulation of fluid flow induced by opposing ac magnetic fields in a continuous casting mold

    SciTech Connect

    Chang, F.C.; Hull, J.R.; Beitelman, L.

    1995-07-01

    A numerical simulation was performed for a novel electromagnetic stirring system employing two rotating magnetic fields. The system controls stirring flow in the meniscus region of a continuous casting mold independently from the stirring induced within the remaining volume of the mold by a main electromagnetic stirrer (M-EMS). This control is achieved by applying to the meniscus region an auxiliary electromagnetic field whose direction of rotation is opposite to that of the main magnetic field produced by the M-EMS. The model computes values and spatial distributions of electromagnetic parameters and fluid flow in the stirred pools of mercury in cylindrical and square geometries. Also predicted are the relationships between electromagnetics and fluid flows pertinent to a dynamic equilibrium of the opposing stirring swirls in the meniscus region. Results of the numerical simulation compared well with measurements obtained from experiments with mercury pools.

  8. A Fast-sampling, Planar Array for Measuring the AC Field of Fermilab Pulsed Extraction Magnets

    SciTech Connect

    DiMarco, E.Joseph; Johnstone, C.; Kiemschies, O.; Kotelnikov, S.K.; Lamm, M.J.; Makulski, A.; Nehring, R.; Orris, D.F.; Russell, A.D.; Tartaglia, Michael Albert; Velev, G.; /Fermilab

    2008-06-25

    A system employing a planar array of inductive pick-up coils has been developed for measurements of the rapidly changing dipole field in pulsed extraction magnets for the Fermilab MuCool project. The magnets are of C-type and deigned to support a peak field of 0.65 T during 8.33 millisecond half-sine pulse at a 15 Hz repetition rate. The coils of the measurement system are fabricated on a single, 97.5 mm wide, 2-layer circuit board. The array of coils is simultaneously sampled at data rates of up to 100 kHz with 10 kHz bandwidth using 24-bit ADC's. A detailed overview of the system and data analysis is presented, along with a characterization of results and system performance.

  9. Magnetoresistive DNA chips based on ac field focusing of magnetic labels

    NASA Astrophysics Data System (ADS)

    Ferreira, H. A.; Cardoso, F. A.; Ferreira, R.; Cardoso, S.; Freitas, P. P.

    2006-04-01

    A study was made on the sensitivity of a magnetoresistive DNA-chip platform being developed for cystic fibrosis diagnostics. The chip, comprised of an array of 2.5×80 μm2 U-shaped spin-valve sensors integrated within current line structures for magnetic label manipulation, enabled the detection at 30 Hz of 250 nm magnetic nanoparticles from 100 pM down to the pM range (or a target DNA concentration of 500 pM). It was observed that the sensor response increased linearly with label concentration. Noise spectra obtained for these sensors showed a thermal noise of 10-17 V2/Hz with a 1/f knee at 50 kHz at a 1 mA sense current, showing that lower detection limits are possible.

  10. Ac-susceptibility investigations of superspin blocking and freezing in interacting magnetic nanoparticle ensembles

    NASA Astrophysics Data System (ADS)

    Botez, Cristian E.; Morris, Joshua L.

    2016-03-01

    We have investigated the effect of dipolar interactions on the superspin blocking and freezing of 9 nm average size Fe3O4 magnetic nanoparticle ensembles. Our dynamic susceptibility data reveals a two-regime behavior of the blocking temperature, T B, upon diluting a Fe3O4/hexane magnetic fluid. As the nanoparticle volume ratio, Φ, is reduced from an as-prepared reference Φ = 1 to Φ = 1/96, the blocking temperature decreases from 46.1 K to 34.2 K, but higher values reenter upon further diluting the magnetic fluid to Φ = 1/384 (where T B = 42.5 K). We found evidence that cooling below T B within the higher concentration range (Φ > 1/48) leads to the collective freezing of the superspins, whereas individual superspin blocking occurs in the presence of weaker interactions (Φ < 1/96). The unexpected increase of the blocking temperature with the decrease of the inter-particle interactions observed at low nanoparticle concentrations is well described by the Mørup-Tronc model.

  11. AC-susceptibility investigations of superspin blocking and freezing in interacting magnetic nanoparticle ensembles

    NASA Astrophysics Data System (ADS)

    Morris, Joshua Logan

    We have investigated the effect of dipolar interactions on the superspin blocking and freezing of 10 nm average size Fe3O4 magnetic nanoparticle ensembles. Our dynamic susceptibility data reveals a two-regime behavior of the blocking temperature, TB, upon diluting a Fe 3O4/hexane magnetic nanoparticle fluid. As the nanoparticle volume ratio, Phi, is reduced from an as-prepared reference Phi = 1 to Phi = 1/96, the blocking temperature decreases from 46.1 K to 34.2 K, but higher values reenter upon further diluting the magnetic fluid to Phi = 1/384 (where TB = 42.5 K). We show that cooling below TB within the higher concentration range (Phi > 1/48) leads to the collective freezing of the superspins in a spin-glass-like fashion, whereas individual superspin blocking occurs in the presence of weaker dipolar interactions (Phi < 1/96). The unexpected increase of the blocking temperature with the decrease of the interparticle interactions observed at low nanoparticle concentrations is well described by the Morup-Tronc (MT) model.

  12. Ac-susceptibility investigations of superspin blocking and freezing in interacting magnetic nanoparticle ensembles.

    PubMed

    Botez, Cristian E; Morris, Joshua L

    2016-03-18

    We have investigated the effect of dipolar interactions on the superspin blocking and freezing of 9 nm average size Fe3O4 magnetic nanoparticle ensembles. Our dynamic susceptibility data reveals a two-regime behavior of the blocking temperature, T(B), upon diluting a Fe3O4/hexane magnetic fluid. As the nanoparticle volume ratio, Φ, is reduced from an as-prepared reference Φ = 1 to Φ = 1/96, the blocking temperature decreases from 46.1 K to 34.2 K, but higher values reenter upon further diluting the magnetic fluid to Φ = 1/384 (where T(B) = 42.5 K). We found evidence that cooling below T B within the higher concentration range (Φ > 1/48) leads to the collective freezing of the superspins, whereas individual superspin blocking occurs in the presence of weaker interactions (Φ < 1/96). The unexpected increase of the blocking temperature with the decrease of the inter-particle interactions observed at low nanoparticle concentrations is well described by the Mørup-Tronc model. PMID:26876797

  13. Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

    SciTech Connect

    Ma, X. Maurer, D. A.; Knowlton, S. F.; ArchMiller, M. C.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; Roberds, N. A.; Traverso, P. J.; Cianciosa, M. R.

    2015-12-15

    Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. The inversion radius of standard sawteeth is used to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.

  14. Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

    NASA Astrophysics Data System (ADS)

    Ma, X.; Maurer, D. A.; Knowlton, S. F.; ArchMiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; Roberds, N. A.; Traverso, P. J.

    2015-12-01

    Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. The inversion radius of standard sawteeth is used to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.

  15. Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

    DOE PAGESBeta

    Ma, X.; Maurer, D. A.; Knowlton, Stephen F.; ArchMiller, M. C.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; et al

    2015-12-22

    Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. Lastly, the inversion radius of standard saw-teeth is usedmore » to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.« less

  16. Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

    SciTech Connect

    Ma, X.; Maurer, D. A.; Knowlton, Stephen F.; ArchMiller, M. C.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; Roberts, N. A.; Traverso, P. J.; Cianciosa, M. R.

    2015-12-22

    Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. Lastly, the inversion radius of standard saw-teeth is used to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.

  17. The effect of external magnetic fields on the catalytic activity of Pd nanoparticles in Suzuki cross-coupling reactions.

    PubMed

    Gao, Lei; Wang, Changlai; Li, Ren; Li, Ran; Chen, Qianwang

    2016-04-14

    Pd nanoparticles supported on Co3[Co(CN)6]2 nanoparticles (marked as Pd@Co3[Co(CN)6]2 nanoparticles) were prepared as catalysts for the Suzuki cross-coupling reaction under external magnetic fields (MFs). It is shown that a weak external MF can increase the rate of the Suzuki cross-coupling reaction at room temperature, and with the increase of the strength of external MFs the reaction rate also increased. At 30 °C, the yield was increased by nearly 50% under a 0.5 T external MF after 24 hours compared to that without a MF applied. Theoretical calculations revealed that the adsorption energy changed from -1.07 to -1.12 eV in the presence of MFs, which increased by 5% compared with the absence of MFs, leading to a lower total energy of the adsorption system, which is beneficial to the reaction. From the analysis of the partial density states, it could be seen that the 2p orbital of the carbon atom in bromobenzene and the 4d orbital of the Pd atom overlap more closely in the presence of MFs, which is beneficial for the electron transfer from the Pd substrate to the bromobenzene molecule. This study is helpful in understanding the interaction between MFs and catalysts and regulating the process of catalytic reactions via MFs. PMID:27043428

  18. Effects of external magnetic field and magnetic anisotropy on chiral spin structures of square nanodisks investigated with a quantum simulation approach

    NASA Astrophysics Data System (ADS)

    Liu, Zhaosen; Ian, Hou

    2016-04-01

    We employed a quantum simulation approach to investigate the magnetic properties of monolayer square nanodisks with Dzyaloshinsky-Moriya (DM) interaction. The computational program converged very quickly, and generated chiral spin structures on the disk planes with good symmetry. When the DM interaction is sufficiently strong, multi-domain structures appears, their sizes or average distance between each pair of domains can be approximately described by a modified grid theory. We further found that the external magnetic field and uniaxial magnetic anisotropy both normal to the disk plane lead to reductions of the total free energy and total energy of the nanosystems, thus are able to stabilize and/or induce the vortical structures, however, the chirality of the vortex is still determined by the sign of the DM interaction parameter. Moreover, the geometric shape of the nanodisk affects the spin configuration on the disk plane as well.

  19. Electric response of a magnetic colloid to periodic external excitation for different nanoparticles concentrations: Determination of the particles' effective charge

    NASA Astrophysics Data System (ADS)

    Batalioto, F.; Barbero, G.; Sehnem, A. L.; Figueiredo Neto, A. M.

    2016-08-01

    The effective electric charge of a nanoparticle in an ionic magnetic colloidal system (an ionic ferrofluid) is determined by using the impedance spectroscopy technique. The electric response of the samples to a harmonic external electric field excitation is described by means of the Poisson-Nernst-Planck model. The model proposed for the theoretical interpretation of the impedance spectroscopy data considers that the magnetic particles are electrically charged with H+ and have in their vicinity Cl- counterions, resulting in an effective charge Qeff. In the presence of an harmonic, in time, external field (frequency bigger than 10 4 Hz ) particles are assumed to be at rest, due to inertial reason. In this framework, the response of the cell is due to the H+ and Cl- present in the solution. From the spectra of the real and imaginary components of the electric impedance of the cell, by means of a best fit procedure to our model, we derive the effective electric charge of the magnetic particles and the bulk density of ions. From an independent measurement of the ζ-potential of the suspension, it is possible to calculate the hydrodynamic radius of the particle, in good agreement with that independently measured.

  20. Large-scale, near-Earth, magnetic fields from external sources and the corresponding induced internal field

    NASA Technical Reports Server (NTRS)

    Langel, R. A.; Estes, R. H.

    1983-01-01

    Data from MAGSAT analyzed as a function of the Dst index to determine the first degree/order spherical harmonic description of the near-Earth external field and its corresponding induced field. The analysis was done separately for data from dawn and dusk. The MAGSAT data was compared with POGO data. A local time variation of the external field persists even during very quiet magnetic conditions; both a diurnal and 8-hour period are present. A crude estimate of Sq current in the 45 deg geomagnetic latitude range is obtained for 1966 to 1970. The current strength, located in the ionosphere and induced in the Earth, is typical of earlier determinations from surface data, although its maximum is displaced in local time from previous results.

  1. Effect of Si addition on AC and DC magnetic properties of (Fe-P)-Si alloy

    NASA Astrophysics Data System (ADS)

    Gautam, Ravi; Prabhu, D.; Chandrasekaran, V.; Gopalan, R.; Sundararajan, G.

    2016-05-01

    We report a new (Fe-P)-Si based alloy with relatively high induction (1.8-1.9 T), low coercivity (< 80 A/m), high resistivity (˜38 μΩ cm) and low core loss (217 W/kg @ 1 T/1 kHz) comparable to the commercially available M530-50 A5 Si-steel. The attractive magnetic and electrical properties are attributed to i) the two phase microstructure of fine nano precipitates of Fe3P dispersed in α-Fe matrix achieved by a two-step heat-treatment process and ii) Si addition enhancing the resistivity of the α-Fe matrix phase. As the alloy processing is by conventional wrought metallurgy method, it has the potential for large scale production.

  2. The effect of nickel content on the ac magnetic properties of 49Fe-49Co-2V alloys

    NASA Astrophysics Data System (ADS)

    Novotny, P. M.

    1988-04-01

    Experimental alloys containing between 0.03 and 0.67 wt. % nickel were produced to determine the effect of low nickel content on the ac magnetic properties of Carpenter's 49Fe-49Co-2V Hiperco (a registered trademark of Carpenter Technology Corp.) 50A alloy. The alloys were processed into 1.02×10-4 m (0.004 in.) thick strip, wound into tape toroids, annealed then tested for core loss at 60 and 400 Hz for induction levels of 1.0, 1.5, and 2.0 T. Toroids annealed at 885 °C in hydrogen, followed by slow cooling, exhibited a linear increase in core loss as nickel content increased due to the presence of a second phase in the microstructure. When the annealing temperature was decreased to 845 °C the second phase was eliminated and the core loss did not vary with nickel content. STEM examination of the samples determined that the second phase was a heavily dislocated bcc α'1 phase which had martensitically transformed from the fcc γ1 phase despite the slow cooling rate. Thermal expansion testing determined that increasing the Ni content in the range of 0-1 wt. % decreased the α1 +γ1 /α1 transformation temperature of the 49Fe-49Co-2V alloy.

  3. Production of large volume, strongly magnetized laser-produced plasmas by use of pulsed external magnetic fields

    SciTech Connect

    Albertazzi, B.; Beard, J.; Billette, J.; Portugall, O.; Ciardi, A.; Vinci, T.; Albrecht, J.; Chen, S. N.; Da Silva, D.; Hirardin, B.; Nakatsutsumi, M.; Romagnagni, L.; Simond, S.; Veuillot, E.; Fuchs, J.; Burris-Mog, T.; Dittrich, S.; Herrmannsdoerfer, T.; Kroll, F.; Nitsche, S.; and others

    2013-04-15

    The production of strongly magnetized laser plasmas, of interest for laboratory astrophysics and inertial confinement fusion studies, is presented. This is achieved by coupling a 16 kV pulse-power system. This is achieved by coupling a 16 kV pulse-power system, which generates a magnetic field by means of a split coil, with the ELFIE laser facility at Ecole Polytechnique. In order to influence the plasma dynamics in a significant manner, the system can generate, repetitively and without debris, high amplitude magnetic fields (40 T) in a manner compatible with a high-energy laser environment. A description of the system and preliminary results demonstrating the possibility to magnetically collimate plasma jets are given.

  4. Production of large volume, strongly magnetized laser-produced plasmas by use of pulsed external magnetic fields.

    PubMed

    Albertazzi, B; Béard, J; Ciardi, A; Vinci, T; Albrecht, J; Billette, J; Burris-Mog, T; Chen, S N; Da Silva, D; Dittrich, S; Herrmannsdörfer, T; Hirardin, B; Kroll, F; Nakatsutsumi, M; Nitsche, S; Riconda, C; Romagnagni, L; Schlenvoigt, H-P; Simond, S; Veuillot, E; Cowan, T E; Portugall, O; Pépin, H; Fuchs, J

    2013-04-01

    The production of strongly magnetized laser plasmas, of interest for laboratory astrophysics and inertial confinement fusion studies, is presented. This is achieved by coupling a 16 kV pulse-power system. This is achieved by coupling a 16 kV pulse-power system, which generates a magnetic field by means of a split coil, with the ELFIE laser facility at Ecole Polytechnique. In order to influence the plasma dynamics in a significant manner, the system can generate, repetitively and without debris, high amplitude magnetic fields (40 T) in a manner compatible with a high-energy laser environment. A description of the system and preliminary results demonstrating the possibility to magnetically collimate plasma jets are given. PMID:23635194

  5. Effect of external magnetic field on IV 99mTc-labeled aminosilane-coated iron oxide nanoparticles: demonstration in a rat model: special report.

    PubMed

    Liberatore, Mauro; Barteri, Mario; Megna, Valentina; D'Elia, Piera; Rebonato, Stefania; Latini, Augusto; De Angelis, Francesca; Scaramuzzo, Francesca Anna; De Stefano, Maria Egle; Guadagno, Noemi Antonella; Chondrogiannis, Sotirios; Maffione, Anna Margherita; Rubello, Domenico; Pala, Alessandro; Colletti, Patrick M

    2015-02-01

    Among the most interesting applications of ferromagnetic nanoparticles (NPs) in medicine is the potential for localizing pharmacologically or radioactively tagged agents directly to selected tissues selected by an adjustable external magnetic field. This concept is demonstrated by the application external magnetic field on IV Tc-labeled aminosilane-coated iron oxide NPs in a rat model. In a model comparing a rat with a 0.3-T magnet over a hind paw versus a rat without a magnet, a static acquisition at 45 minutes showed that 27% of the administered radioactivity was in the area subtended by the magnet, whereas the liver displays a percentage of binding of 14% in the presence of the magnet and of 16% in the absence of an external magnetic field. These preliminary results suggest that the application of an external magnetic field may be a viable route for the development of methods for the confinement of magnetic NPs labeled with radioactive isotopes targeted for predetermined sites of the body. PMID:25551623

  6. Coherent States for the Two-Dimensional Dirac-Moshinsky Oscillator Coupled to an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Ojeda-Guillén, D.; Mota, R. D.; Granados, V. D.

    2015-03-01

    We show that the (2+1)-dimensional Dirac-Moshinsky oscillator coupled to an external magnetic field can be treated algebraically with the SU(1,1) group theory and its group basis. We use the su(1,1) irreducible representation theory to find the energy spectrum and the eigenfunctions. Also, with the su(1,1) group basis we construct the relativistic coherent states in a closed form for this problem. Supported by SNI-México, COFAA-IPN, EDI-IPN, EDD-IPN, SIP-IPN project number 20140598

  7. External Weighing with Analytical Balances: Determination of Magnetic Susceptibility of Inorganic Compounds.

    ERIC Educational Resources Information Center

    Toma, Henrique E.; And Others

    1983-01-01

    An approach is described in which accurate weighings are provided under circumstances when samples cannot be placed directly on a balance pan. The approach, based on external weighing, uses a new simple apparatus designed for any kind of analytical balance and not requiring a hole through the base of the balance. (JN)

  8. Advanced single permanent magnet axipolar ironless stator ac motor for electric passenger vehicles

    NASA Technical Reports Server (NTRS)

    Beauchamp, E. D.; Hadfield, J. R.; Wuertz, K. L.

    1983-01-01

    A program was conducted to design and develop an advanced-concept motor specifically created for propulsion of electric vehicles with increased range, reduced energy consumption, and reduced life-cycle costs in comparison with conventional systems. The motor developed is a brushless, dc, rare-earth cobalt, permanent magnet, axial air gap inductor machine that uses an ironless stator. Air cooling is inherent provided by the centrifugal-fan action of the rotor poles. An extensive design phase was conducted, which included analysis of the system performance versus the SAE J227a(D) driving cycle. A proof-of-principle model was developed and tested, and a functional model was developed and tested. Full generator-level testing was conducted on the functional model, recording electromagnetic, thermal, aerodynamic, and acoustic noise data. The machine demonstrated 20.3 kW output at 1466 rad/s and 160 dc. The novel ironless stator demonstated the capability to continuously operate at peak current. The projected system performance based on the use of a transistor inverter is 23.6 kW output power at 1466 rad/s and 83.3 percent efficiency. Design areas of concern regarding electric vehicle applications include the inherently high windage loss and rotor inertia.

  9. Quantum-classical transition of the escape rate of a biaxial ferromagnetic spin with an external magnetic field

    NASA Astrophysics Data System (ADS)

    Owerre, S. A.; Paranjape, M. B.

    2014-05-01

    We study the model of a biaxial single ferromagnetic spin Hamiltonian with an external magnetic field applied along the medium axis. The phase transition of the escape rate is investigated. Two different but equivalent methods are implemented. Firstly, we derive the semi-classical description of the model which yields a potential and a coordinate dependent mass. Secondly, we employ the method of spin-particle mapping which yields a similar potential to that of semi-classical description but with a constant mass. The exact instanton trajectory and its corresponding action, which have not been reported in any literature is being derived. Also, the analytical expressions for the first- and second-order crossover temperatures at the phase boundary are derived. We show that the boundary between the first-and the second-order phase transitions is greatly influenced by the magnetic field.

  10. Equation of State of the Strong Interaction Matter in an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Zhang, Rui; Liu, Yu-Xin

    2015-10-01

    We investigate the equation of state of the strong interaction matter in a background magnetic field via the two flavor Nambu-Jona-Lasinio model. Starting from the mean-field thermodynamical potential density Ω, we calculate the pressure density p, the entropy density s, the energy density ɛ, and the interaction measure (ɛ - 3p)/T4 of the strong interaction matter at finite temperature and finite magnetic field. The results manifest that the chiral phase transition is just a crossover but not a low order phase transition. Moreover there may exist magnetic catalysis effect, and its mechanism is just the effective dimension reduction induced by the magnetic field. Supported by the National Natural Science Foundation of China under Grant Nos. 10935001, 11175004 and 11435001, and the National Key Basic Research Program of China under Grant Nos. G2013CB834400 and 2015CB856900

  11. Using genetic algorithms to characterize ferrofluid topographies in externally applied magnetic fields

    NASA Astrophysics Data System (ADS)

    Spinella-Mamo, V.; Paranjape, M.

    2009-02-01

    Both ferrofluidics and genetic algorithms are relatively new fields. Due to complex physical interactions, ferrofluidic topographies and assemblies have only been solved using finite time step, Lattice Boltzmann, and finite-element methods in very simple magnetic field configurations. In this paper, we show that it is possible (and highly advantageous) to employ genetic algorithms to solve for the fluid topographies, which can be extended to include more complex magnetic fields.

  12. Enhancement of Laser Induced Breakdown Emission in the Presence of External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Rai, Virendra N.; Zhang, Hansheng; Yueh, Fang Y.; Singh, Jagdish P.

    2001-04-01

    Laser induced breakdown spectroscopy (LIBS) is a useful method for determining the elemental composition in solid, liquid and gaseous samples. Elemental analysis of sample is accomplished by measuring the emission of the elemental atom or ions present in the plasma from any kind of samples. The ability to form and study the plasma on unprepared sample makes LIBS a very attractive analytical technique. Various techniques have been used for enhancing the analytical characteristics of the plasma sources used for elemental analysis. Many complicated magnetic field geometries have been used earlier with various types of plasma sources to enhance the plasma emission. In this paper characterization of laser induced plasma emission from Manganese (Mn) in liquid solution is presented. The plasma was formed in between the poles of two magnets with 1200 Gauss pole strength separated by 5 mm. The effect of magnetic field on various emission properties was studied. An one and half times enhancement in the intensity of Mn emission line at 403.076, 403.307 and 403.449 nm was observed for the laser intensity below 1.5x10e12 W/cm2. The intensity of Mn line decreases at higher laser intensity in the presence of magnetic field. This decrease in the emission at higher laser intensity seems to be due to turbulence as a result of laser induced shock as well as generation of instability in the plasma in the presence of magnetic field. The calibration curve for Mn was obtained in an optimized condition in the absence and presence of magnetic field. The limit of detection for Mn in liquid was found to be 0.63 PPM in the presence of magnetic field, which is less in comparison to the absence of magnetic field ( 0.87 PPM). * Visiting Scientist from Centre for Advanced Technology, Indore-452 013 (INDIA)

  13. On the role of the interactions of ions with external magnetic fields in physiologic processes and their importance in chronobiology.

    PubMed

    Ulmer, W

    2002-01-01

    Homage to the scientific work of Franz Halberg is inevitably connected with the development and importance of chronobiology and its applications in chronomedicine. We show that nonlinear reaction-diffusion systems with feedsideward coupling give rise to oscillations between different limit cycles favoring either inhibition or stimulation of the growth or decay of a component. The inclusion of the diffusion part of each concentration distribution offers the possibility of also taking into account the interaction of charged constituents with external magnetic fields. Concentration oscillations between different limit cycles of the constituents can thus be stabilized. It is assumed that the z-component of the external magnetic field is related to the rather weak solar magnetic field (ca. 10(-9) Tesla). Periods of about one week result for some positive (Mg2+, Ca2+, K+) and negative (e.g. Cl-) ions and some organic acids containing phosphates. The resonance time of a free proton H+ determining the oscillations of the pH-value is about 1 day and that of OH1 is about 3.5 days (half a week). The influence of the geomagnetic field (x- or y-component) in the same range is of a few to ca. 20-30 minutes in the case of charged proteins. An essential condition for this separation is that in general the geomagnetic field does not coincide with the z-component of the solar magnetic field. As an example, the role of the timedependence of the growth and ATP-concentration of the irradiation of the tumor spheroid C3H-MA (mammary adenocarcinoma of mice) is presented. PMID:11980358

  14. Magnetoelectric effect and phase transitions in CuO in external magnetic fields

    PubMed Central

    Wang, Zhaosheng; Qureshi, Navid; Yasin, Shadi; Mukhin, Alexander; Ressouche, Eric; Zherlitsyn, Sergei; Skourski, Yurii; Geshev, Julian; Ivanov, Vsevolod; Gospodinov, Marin; Skumryev, Vassil

    2016-01-01

    Apart from being so far the only known binary multiferroic compound, CuO has a much higher transition temperature into the multiferroic state, 230 K, than any other known material in which the electric polarization is induced by spontaneous magnetic order, typically lower than 100 K. Although the magnetically induced ferroelectricity of CuO is firmly established, no magnetoelectric effect has been observed so far as direct crosstalk between bulk magnetization and electric polarization counterparts. Here we demonstrate that high magnetic fields of ≈50 T are able to suppress the helical modulation of the spins in the multiferroic phase and dramatically affect the electric polarization. Furthermore, just below the spontaneous transition from commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213 K, even modest magnetic fields induce a transition into the incommensurate structure and then suppress it at higher field. Thus, remarkable hidden magnetoelectric features are uncovered, establishing CuO as prototype multiferroic with abundance of competitive magnetic interactions. PMID:26776921

  15. Theoretical analysis of ferromagnetic microparticles in streaming liquid under the influence of external magnetic forces

    NASA Astrophysics Data System (ADS)

    Brandl, Martin; Mayer, Michael; Hartmann, Jens; Posnicek, Thomas; Fabian, Christian; Falkenhagen, Dieter

    2010-09-01

    The microsphere based detoxification system (MDS) is designed for high specific toxin removal in extracorporeal blood purification using functionalized microparticles. A thin wall hollow fiber membrane filter separates the microparticle-plasma suspension from the bloodstream. For patient safety, it is necessary to have a safety system to detect membrane ruptures that could lead to the release of microparticles into the bloodstream. A non-invasive optical detection system including a magnetic trap is developed to monitor the extracorporeal venous bloodstream for the presence of released microparticles. For detection, fluorescence-labeled ferromagnetic beads are suspended together with adsorbent particles in the MDS circuit. In case of a membrane rupture, the labeled particles would be released into the venous bloodstream and partly captured by the magnetic trap of the detector. A physical model based on fluidic, gravitational and magnetic forces was developed to simulate the motion and sedimentation of ferromagnetic particles in a magnetic trap. In detailed simulation runs, the concentrations of accumulated particles under different applied magnetic fields within the magnetic trap are shown. The simulation results are qualitatively compared with laboratory experiments and show excellent accordance. Additionally, the sensitivity of the particle detection system is proofed in a MDS laboratory experiment by simulation of a membrane rupture.

  16. Magnetoelectric effect and phase transitions in CuO in external magnetic fields.

    PubMed

    Wang, Zhaosheng; Qureshi, Navid; Yasin, Shadi; Mukhin, Alexander; Ressouche, Eric; Zherlitsyn, Sergei; Skourski, Yurii; Geshev, Julian; Ivanov, Vsevolod; Gospodinov, Marin; Skumryev, Vassil

    2016-01-01

    Apart from being so far the only known binary multiferroic compound, CuO has a much higher transition temperature into the multiferroic state, 230 K, than any other known material in which the electric polarization is induced by spontaneous magnetic order, typically lower than 100 K. Although the magnetically induced ferroelectricity of CuO is firmly established, no magnetoelectric effect has been observed so far as direct crosstalk between bulk magnetization and electric polarization counterparts. Here we demonstrate that high magnetic fields of ≈ 50 T are able to suppress the helical modulation of the spins in the multiferroic phase and dramatically affect the electric polarization. Furthermore, just below the spontaneous transition from commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213 K, even modest magnetic fields induce a transition into the incommensurate structure and then suppress it at higher field. Thus, remarkable hidden magnetoelectric features are uncovered, establishing CuO as prototype multiferroic with abundance of competitive magnetic interactions. PMID:26776921

  17. Second VAMAS a.c. loss measurement intercomparison: magnetization measurement of low-frequency (hysteretic) a.c. loss in NbTi multifilamentary strands

    NASA Astrophysics Data System (ADS)

    Collings, E. W.; Sumption, M. D.; Itoh, K.; Wada, H.; Tachikawa, K.

    The results of the 2 nd VAMAS measurement intercomparison program on low-frequency (hysteretic) a.c. loss are presented and discussed. Two sets of multifilamentary NbTi strands (Set No. 1: copper matrix, fil. diams 0.5, 1, 3, and 12 μm; Set No. 2: cupronickel matrix, fil. diams 0.4, 0.5, and 1 μm) were subjected to interlaboratory testing. In an initial series of tests, samples in various forms (e.g. wire bundles, coils) were measured mostly by vibrating-sample- and SQUID magnetometry. Considerable scatter was noted especially in the small-filament-diameter a.c.-loss data. In a study of measurement accuracy, a supplementary series of tests compared the results of VSM measurement of a given pair of copper-matrix samples. In the light of all the results, factors contributing to a.c. loss error are discussed and recommendations are made concerning the specification of future a.c.-loss measurement intercomparisons.

  18. Forced magnetic reconnection and field penetration of an externally applied rotating helical magnetic field in the TEXTOR tokamak.

    PubMed

    Kikuchi, Y; de Bock, M F M; Finken, K H; Jakubowski, M; Jaspers, R; Koslowski, H R; Kraemer-Flecken, A; Lehnen, M; Liang, Y; Matsunaga, G; Reiser, D; Wolf, R C; Zimmermann, O

    2006-08-25

    The magnetic field penetration process into a magnetized plasma is of basic interest both for plasma physics and astrophysics. In this context special measurements on the field penetration and field amplification are performed by a Hall probe on the dynamic ergodic divertor (DED) on the TEXTOR tokamak and the data are interpreted by a two-fluid plasma model. It is observed that the growth of the forced magnetic reconnection by the rotating DED field is accompanied by a change of the plasma fluid rotation. The differential rotation frequency between the DED field and the plasma plays an important role in the process of the excitation of tearing modes. The momentum input from the rotating DED field to the plasma is interpreted by both a ponderomotive force at the rational surface and a radial electric field modified by an edge ergodization. PMID:17026312

  19. Common effect of chemical and external pressures on the magnetic properties of RCoPO (R = La, Pr)

    NASA Astrophysics Data System (ADS)

    Prando, G.; Bonfà, P.; Profeta, G.; Khasanov, R.; Bernardini, F.; Mazzani, M.; Brüning, E. M.; Pal, A.; Awana, V. P. S.; Grafe, H.-J.; Büchner, B.; De Renzi, R.; Carretta, P.; Sanna, S.

    2013-02-01

    We report a detailed investigation of RCoPO (R = La, Pr) and LaCoAsO materials performed by means of muon spin spectroscopy. Zero-field measurements show that the electrons localized on the Pr3+ ions do not play any role in the static magnetic properties of the compounds. Magnetism at the local level is indeed fully dominated by the weakly itinerant ferromagnetism from the Co sublattice only. The increase of the chemical pressure triggered by the different ionic radii of La3+ and Pr3+, on the other hand, plays a crucial role in enhancing the value of the magnetic critical temperature and can be mimicked by the application of external hydrostatic pressure up to 24 kbar. A sharp discontinuity in the local magnetic field at the muon site in LaCoPO at around 5 kbar suggests a sizable modification in the band structure of the material upon increasing pressure. This scenario is qualitatively supported by ab initio density-functional-theory calculations.

  20. Fracture problem for an external circumferential crack in a functionally graded superconducting cylinder subjected to a parallel magnetic field

    NASA Astrophysics Data System (ADS)

    Yan, Z.; Gao, S. W.; Feng, W. J.

    2016-02-01

    In this study, the multiple isoparametric finite element method (MIFEM) is used to investigate external circumferential crack problem of a functionally graded superconducting cylinder subjected to electromagnetic forces. The superconducting cylinder is composed by Bi2223/Ag composite with material parameters varying. A crack reference region is defined to reflect the effects of crack on flux and current densities, and the magnetically impermeable crack surface condition and the generalized Irie-Yamafuji critical state model outside the crack region are adopted. The distributions of magnetic flux density in the superconducting cylinder are obtained analytically for both the zero-field cooling (ZFC) and the field cooling (FC) activation processes. Based on the MIFEM, the stress intensity factors (SIFs) at crack fronts in the process of field ascent and/or descent are then numerically calculated. It is interesting to note from numerical results that for the present crack model in the ZFC activation process, the crack is easily propagate and grow with the applied field increases, and that in the field descent process of either the ZFC case or FC case, the crack generally does not propagate. In addition, in the field ascent process of the ZFC case, the SIFs depend on not only the crack depths and model parameters but also the applied field. The present study should be helpful to the design and application of high-temperature superconductors with external edge cracks.

  1. Direct observation of electronic and nuclear ground state splitting in external magnetic field by inelastic neutron scattering on oxidized ferrocene and ferrocene containing polymers

    NASA Astrophysics Data System (ADS)

    Appel, Markus; Frick, Bernhard; Elbert, Johannes; Gallei, Markus; Stühn, Bernd

    2015-01-01

    The quantum mechanical splitting of states by interaction of a magnetic moment with an external magnetic field is well known, e.g., as Zeeman effect in optical transitions, and is also often seen in magnetic neutron scattering. We report excitations observed in inelastic neutron spectroscopy on the redox-responsive polymer poly(vinylferrocene). They are interpreted as splitting of the electronic ground state in the organometallic ferrocene units attached to the polymer chain where a magnetic moment is created by oxidation. In a second experiment using high resolution neutron backscattering spectroscopy we observe the hyperfine splitting, i.e., interaction of nuclear magnetic moments with external magnetic fields leading to sub-μeV excitations observable in incoherent neutron spin-flip scattering on hydrogen and vanadium nuclei.

  2. Automated ac galvanomagnetic measurement system

    NASA Technical Reports Server (NTRS)

    Szofran, F. R.; Espy, P. N.

    1985-01-01

    An automated, ac galvanomagnetic measurement system is described. Hall or van der Pauw measurements in the temperature range 10-300 K can be made at a preselected magnetic field without operator attendance. Procedures to validate sample installation and correct operation of other system functions, such as magnetic field and thermometry, are included. Advantages of ac measurements are discussed.

  3. Equilibrium configurations of a jet of an ideally conducting liquid in an external nonuniform magnetic field

    NASA Astrophysics Data System (ADS)

    Zubarev, N. M.; Zubareva, O. V.

    2016-06-01

    Possible equilibrium configurations of the free surface of a jet of an ideally conducting liquid placed in a nonuniform magnetic field are considered. The magnetic field is generated by two thin wires that are parallel to the jet and bear oppositely directed currents. Equilibrium is due to a balance between capillary and magnetic forces. For the plane symmetric case, when the jet deforms only in the plane of its cross section, two one-parameter families of exact solutions to the problem are derived using the method of conformal mapping. According to these solutions, a jet with an initially circular cross section deforms up to splitting into two separate jets. A criterion for jet splitting is derived by analyzing approximate two-parameter solutions.

  4. Nucleon-nucleon scattering in a strong external magnetic field and the neutrino emissivity

    SciTech Connect

    Bavarsad, E.; Mohammadi, R.; Haghighat, M.

    2010-11-15

    The nucleon-nucleon scattering in a large magnetic background is considered to find its potential to change the neutrino emissivity of the neutron stars. For this purpose, we consider the one-pion-exchange approximation to find the nucleon-nucleon (NN) cross section in a background field as large as 10{sup 15}-10{sup 18} G. We show that the NN cross section in neutron stars with temperatures in the range 0.1-5 MeV can be changed up to the 1 order of magnitude with respect to the one in the absence of the magnetic field. In the limit of the soft neutrino emission, the neutrino emissivity can be written in terms of the NN-scattering amplitude; therefore, the large magnetic fields can dramatically change the neutrino emissivity of the neutron stars as well.

  5. Plasma jets subject to adjustable current polarities and external magnetic fields

    NASA Astrophysics Data System (ADS)

    Byvank, Tom; Schrafel, Peter; Gourdain, Pierre; Seyler, Charles; Kusse, Bruce

    2014-12-01

    In the present research, collimated plasma jets form from ablation of a radial foil (Al 20 μm thin disk) using a pulsed power generator (COBRA) with 1 MA peak current and 100 ns rise time. Plasma dynamics of the jet are diagnosed with and without an applied uniform axial magnetic field (1 T) and under a change of current polarities, which correspond to current moving either radially outward or inward from the foil's central axis. Experimental results are compared with numerical simulations (PERSEUS). The influence of the Hall effect on the jet development is observed under opposite current polarities. Additionally, the magnetic field compression within the jet is examined. Further studies will compare the laboratory-generated plasma jets and astrophysical jets with embedded magnetic fields.

  6. Electromagnetically induced transparency in a two-dimensional quantum pseudo-dot system: Effects of geometrical size and external magnetic field

    NASA Astrophysics Data System (ADS)

    Jahromi, Alaeddin Sayahian; Rezaei, G.

    2015-01-01

    Electromagnetically induced transparency in a two-dimensional quantum pseudo-dot system, under the influence of a uniform magnetic field, is theoretically investigated. In this regard, the effects of external magnetic field and the geometrical size of the pseudo-dot system on the absorption as well as refractive index and the group velocity of the probe light pulse are investigated. The results show that the electromagnetically induced transparency occurs in the system and its frequency, transparency window and group velocity of the probe field are affected by the external magnetic field and the geometrical size of the pseudo-dot system. Also, electromagnetically induced transparency and the group velocity of light can be controlled via the external magnetic field and geometrical size.

  7. The effect of external magnetic fields on the catalytic activity of Pd nanoparticles in Suzuki cross-coupling reactions

    NASA Astrophysics Data System (ADS)

    Gao, Lei; Wang, Changlai; Li, Ren; Li, Ran; Chen, Qianwang

    2016-04-01

    Pd nanoparticles supported on Co3[Co(CN)6]2 nanoparticles (marked as Pd@Co3[Co(CN)6]2 nanoparticles) were prepared as catalysts for the Suzuki cross-coupling reaction under external magnetic fields (MFs). It is shown that a weak external MF can increase the rate of the Suzuki cross-coupling reaction at room temperature, and with the increase of the strength of external MFs the reaction rate also increased. At 30 °C, the yield was increased by nearly 50% under a 0.5 T external MF after 24 hours compared to that without a MF applied. Theoretical calculations revealed that the adsorption energy changed from -1.07 to -1.12 eV in the presence of MFs, which increased by 5% compared with the absence of MFs, leading to a lower total energy of the adsorption system, which is beneficial to the reaction. From the analysis of the partial density states, it could be seen that the 2p orbital of the carbon atom in bromobenzene and the 4d orbital of the Pd atom overlap more closely in the presence of MFs, which is beneficial for the electron transfer from the Pd substrate to the bromobenzene molecule. This study is helpful in understanding the interaction between MFs and catalysts and regulating the process of catalytic reactions via MFs.Pd nanoparticles supported on Co3[Co(CN)6]2 nanoparticles (marked as Pd@Co3[Co(CN)6]2 nanoparticles) were prepared as catalysts for the Suzuki cross-coupling reaction under external magnetic fields (MFs). It is shown that a weak external MF can increase the rate of the Suzuki cross-coupling reaction at room temperature, and with the increase of the strength of external MFs the reaction rate also increased. At 30 °C, the yield was increased by nearly 50% under a 0.5 T external MF after 24 hours compared to that without a MF applied. Theoretical calculations revealed that the adsorption energy changed from -1.07 to -1.12 eV in the presence of MFs, which increased by 5% compared with the absence of MFs, leading to a lower total energy of the

  8. Treatment of the external epicondylitis of the humerus with a magnetic field

    NASA Technical Reports Server (NTRS)

    Degen, I. L.

    1974-01-01

    The therapeutic effect of a constant and varying magnetic field on epicondylitis of the humerus is studied on ninety patients. Good results are obtained from the treatment (recovery of 80%, considerable improvement in 14.5%). The method is recommended for clinical application.

  9. Interaction of laser radiation with plasma under the MG external magnetic field

    NASA Astrophysics Data System (ADS)

    Ivanov, V. V.; Maximov, A. V.; Covington, A. M.; Wiewior, P. P.; Astanovitskiy, A. L.; Nalajala, V.; Chalyy, O.; Dmitriev, O.

    2015-11-01

    A strong magnetic field can dramatically change the properties of plasmas. Studies of plasmas in the magnetic field are important for basic physics, astrophysics, and controlled fusion. A series of shots was carried out at the 1 MA pulsed power generator coupled with a 50-TW laser. A 2-2.5 MG magnetic field was generated on the surface of the Al 1 mm rod load by 1 MA current. A sub-nanosecond laser pulse with intensity of 3x1015 W/cm2 was focused on the load surface. A collimated plasma jet 1-3 mm long was observed propagating back from the focal spot with a speed of 240 km/s. Another plasma jet was seen on the rear side of the rod load. Both jets on the front and rear sides were also seen in shots with the 0.8 mm Cu load. The front plasma jet may be linked to the ExB drift observed elsewhere at smaller B-fields. The enhanced temperature and keV x-ray radiation of laser plasma in the magnetic field were found with x-ray spectroscopy. Work was supported by the DOE grant DE-SC0008824 and DOE/NNSA UNR grant DE-FC52-06NA27616.

  10. Non-axisymmetric magneto- hydrodynamic equilibrium in the presence of internal magnetic islands and external magnetic perturbation coils

    NASA Astrophysics Data System (ADS)

    Tobias, B. J.; Austin, M. E.; Classen, I. G. J.; Domier, C. W.; Luhmann, N. C., Jr.; Park, J.-K.; Paz-Soldan, C.; Turnbull, A. D.; Yu, L.; the DIII-D Team

    2013-12-01

    Non-axisymmetric equilibria arise in DIII-D discharges that are subjected to magnetic perturbation by 3D magnetic coils. But, 3D shaping of the entire plasma, including the boundary, also occurs in the rotating fluid frame of saturated internal magnetic islands (Tobias et al 2013 Plasma Phys. Control. Fusion 55 095006). This is advantageous since internal islands and kink responses that rotate near the fluid velocity of the plasma are easily diagnosed, while static perturbations in the laboratory frame are not. The helicity of the perturbed shape is the same in both rotational frames of reference, making one mode a diagnostic proxy for the other and allowing internal modes to be used as a source of data for comparison to models typically applied to understanding the effect of static perturbations. Discrepancies with ideal magneto-hydrodynamic equilibrium obtained by the IPEC (Park et al 2007 Phys. Plasmas 14 052110) method brings attention to the treatment of plasma displacements near rational surfaces and their relationship to the accessibility of equilibrium states.

  11. Broad band simulation of Gamma Ray Bursts (GRB) prompt emission in presence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    Ziaeepour, Houri; Gardner, Brian

    2011-12-01

    The origin of prompt emission in GRBs is not yet well understood. The simplest and most popular model is Synchrotron Self-Compton (SSC) emission produced by internal shocks inside an ultra-relativistic jet. However, recent observations of a delayed high energy component by the Fermi-LAT instrument have encouraged alternative models. Here we use a recently developed formulation of relativistic shocks for GRBs to simulate light curves and spectra of synchrotron and self-Compton emissions in the framework of internal shock model. This model takes into account the evolution of quantities such as densities of colliding shells, and fraction of kinetic energy transferred to electrons and to induced magnetic field. We also extend this formulation by considering the presence of a precessing external magnetic field. These simulations are very realistic and present significant improvement with respect to previous phenomenological GRB simulations. They reproduce light curves of separate peaks of real GRBs and variety of spectral slopes at E > Epeak observed by the Fermi-LAT instrument. The high energy emission can be explained by synchrotron emission and a subdominant contribution from inverse Compton. We also suggest an explanation for extended tail emission and relate it to the screening of the magnetic field and/or trapping of accelerated electrons in the electromagnetic energy structure of the plasma in the shock front. Spectral slopes of simulated bursts at E << Epeak are consistent with theoretical prediction and at E < Epeak can be flatter if the spectrum of electrons is roughly flat or has a shallow slope at low energies. The observed flat spectra at soft gamma-ray and hard x-ray bands is the evidence that there is a significant contribution at E < Epeak from lower Lorentz factor wing of electron distribution which have a roughly random acceleration rather than being thermal. This means that the state of matter in the jet at the time of ejection is most probably

  12. Superparamagnetic state by linear and non-linear AC magnetic susceptibility in Mn0.5Zn0.5Fe2O4 ferrites nanoparticles.

    PubMed

    Suneetha, T; Kundu, S; Kashyap, Subhash C; Gupta, H C; Nath, T K

    2013-01-01

    The Mn0.5Zn0.5Fe2O4 nanoparticles has been synthesized using citrate-gel-precursor method. The direct mixing of nitrates and acetates yields homogeneous nanoparticles. Phase formation and crystal structure of the synthesized powder were examined through the X-ray diffraction (XRD). Fourier transform infrared (FTIR) spectra of the sample confirm the spinel structure. The average particle size was determined by transmission electron microscopy (TEM) and field emission scanning electron microscopy (FESEM). The average particle size is found to be about 13 nm. Superparamagnetic-like nature of the nanoparticles of Mn0.5Zn0.5Fe2O4 has been revealed through various dc and linear and non-linear ac magnetization measurements. However, the nanoparticles do not behave like ideal non-interacting superparamagnets. The magnetic particle size is found to be about 8 nm with saturation magnetization about 18.1 emu/g. The blocking temperature (T(B)) of the nanoparticle assembly is found to be about 150 K as observed from dc and ac magnetization measurements. The frequency dependence of the blocking temperature (T(B)) is found to follow Vogel-Fulcher law. The associated characteristic time tau0 is found to be 10(-5) s. This value is different from that generally found for non-interacting superparamagnetic (SPM) systems (tau0 = 10(-9)-10(-10) s). PMID:23646726

  13. External magnetic field effect on the growth rate of a plasma-loaded free-electron laser

    NASA Astrophysics Data System (ADS)

    Esmaeildoost, N.; Jafari, S.; Abbasi, E.

    2016-06-01

    In order to extend the production of intense coherent radiation to angstrom wavelengths, a laser wave is employed as a laser wiggler which propagates through a magnetized plasma channel. The plasma-loaded laser wigglers increase the ability of laser guidance and electron bunching process compared to the counterpropagating laser wigglers in vacuum. The presence of the plasma medium can make it possible to propagate the laser wiggler and the electron beam parallel to each other so that the focusing of the pulse will be saved. In addition, employing an external guide magnetic field can confine both the ambient plasma and the transverse motions of the electron beam, therefore, improving the free-electron lasers' efficiency, properly. Electron trajectories have been obtained by solving the steady state equations of motion for a single particle and the fourth-order Runge-Kutta method has been used to simulate the electron orbits. To study the growth rate of a laser-pumped free-electron laser in the presence of a plasma medium, perturbation analysis has been performed to combine the momentum transfer, continuity, and wave equations, respectively. Numerical calculations indicate that by increasing the guide magnetic field frequency, the growth rate for group I orbits increases, while for group II and III orbits decreases.

  14. Orbital motion in generalized static fields of FELs accounting for axial magnetic field, beam forces, undulator and external focusing

    SciTech Connect

    Papadichev, V.A.

    1995-12-31

    Various types of undulators with or without axial magnetic field are used in FELs. Supplementary beam focusing can be applied by wedging, inclining or profiling pole faces of plan undulators or superposing external focusing magnetic fields in addition to undulator own focusing. Space-charge forces influence significantly particle motion in high-current, low-energy electron beams. Finally, one can use simultaneously two or more different undulators for some specific purpose: more efficient and selective higher harmonics generation, changing polarization types and direction, gain enhancement in double-period undulator etc. All these cases can be treated by solving the generalized equations of transverse orbital motion in a linear approximation, which is widely used for orbit calculation, gives sufficient accuracy for practical purposes and allows to consider many variants and optimize the chosen one. The undulator field is described as a field of two plane undulators with mutually orthogonal fields and an arbitrary axial (phase) shift between them. Various values of the phase shift correspond to right- or left-handed helical undulators, plane undulator of different polarization etc. The general formulae are reduced to forms that allow easier examination of particular cases: planar or helical undulator combined with axial magnetic field or without it, gyroresonance, limiting beam current, polarization etc.

  15. Theory and simulation of quasilinear transport from external magnetic field perturbations in a DIII-D plasma

    NASA Astrophysics Data System (ADS)

    Waltz, R. E.; Ferraro, N. M.

    2015-04-01

    The linear response profiles for the 3D perturbed magnetic fields, currents, ion velocities, plasma density, pressures, and electric potential from low-n external resonant magnetic field perturbations (RMPs) are obtained from the collisional two-fluid M3D-C1 code [N. M. Ferraro and S. C. Jardin, J. Comput. Phys. 228, 7742 (2009)]. A newly developed post-processing RMPtran code computes the resulting quasilinear E×B and magnetic (J×B) radial transport flows with respect to the unperturbed flux surfaces in all channels. RMPtran simulations focus on ion (center of mass) particle and transient non-ambipolar current flows, as well as the toroidal angular momentum flow. The paper attempts to delineate the RMP transport mechanisms that might be responsible for the RMP density pump-out seen in DIII-D [M. A. Mahdavi and J. L. Luxon, Fusion Sci. Technol. 48, 2 (2005)]. Experimentally, the starting high toroidal rotation does not brake to a significantly lower rotation after the pump-out suggesting that convective and E×B transport mechanisms dominate. The direct J×B torque from the transient non-ambipolar radial current expected to accelerate plasma rotation is shown to cancel much of the Maxwell stress J×B torque expected to brake the plasma rotation. The dominant E×B Reynolds stress accelerates rotation at the top of the pedestal while braking rotation further down the pedestal.

  16. Chiral and parity symmetry breaking for planar fermions: Effects of a heat bath and uniform external magnetic field

    SciTech Connect

    Ayala, Alejandro; Bashir, Adnan; Gutierrez, Enif; Raya, Alfredo; Sanchez, Angel

    2010-09-01

    We study chiral symmetry breaking for relativistic fermions, described by a parity-violating Lagrangian in 2+1-dimensions, in the presence of a heat bath and a uniform external magnetic field. Working within their four-component formalism allows for the inclusion of both parity-even and -odd mass terms. Therefore, we can define two types of fermion antifermion condensates. For a given value of the magnetic field, there exist two different critical temperatures which would render one of these condensates identically zero, while the other would survive. Our analysis is completely general: it requires no particular simplifying hierarchy among the energy scales involved, namely, bare masses, field strength, and temperature. However, we do reproduce some earlier results, obtained or anticipated in literature, corresponding to special kinematical regimes for the parity conserving case. Relating the chiral condensate to the one-loop effective Lagrangian, we also obtain the magnetization and the pair production rate for different fermion species in a uniform electric field through the replacement B{yields}-iE.

  17. Dust Lattice Waves in Two-Dimensional Hexagonal Dust Crystals with an External Magnetic Field

    SciTech Connect

    Farokhi, B.; Shahmansouri, M.

    2008-09-07

    The influence of a constant magnetic field on the propagation of dust-lattice (DL) modes in a two-dimensional hexagonal strongly coupled plasma crystal formed by paramagnetic particles is considered. The expression for the wave dispersion relation clearly shows that high-frequency and low-frequency branches exist as a result of the coupling of longitudinal and transverse modes due to the Lorentz force acting on the dust particles.

  18. AC Magnetic Susceptibility of the Assembled-Metal Complex {NBu4[FeIIFeIII(ox)3]}∞ (Bu=n-C4H9, ox=oxalato)

    NASA Astrophysics Data System (ADS)

    Bhattacharjee, Ashis; Nakazawa, Yasuhiro; Kobayashi, Hayao; Sorai, Michio

    2002-09-01

    AC magnetic susceptibility (χAC=χ\\prime-iχ\\prime\\prime) of {NBu4[FeIIFeIII(ox)3]}∞ was measured in the 4-50 K range for different frequencies (0.1-1000 Hz). Both of the χ\\prime(T) and χ\\prime\\prime(T) plots showed two peaks in two temperature regions: 4-33 K and 33-50 K. The χ\\prime(T) and χ\\prime\\prime(T) peaks in the 33-50 K range can be associated with the magnetic phase transition at the Néel temperature (43.3 K). However, the χ\\prime(T) peak in the 4-33 K range was found to be shifted towards lower temperature from 15.5 K to 13.5 K with increasing frequency, accompanied by a decrease in peak height. The fractional relative change in the peak temperature per decade change in frequency was calculated. The χ\\prime\\prime(T) in the 4-33 K range exhibited a broad peak around 25 K. The frequency dependence of χ\\prime(T) and χ\\prime\\prime(T) in the 4-33 K range occurred in the region where the irreversibilities in the ZFC (zero-field-cooled)-FC (field cooled) susceptibilities appeared. In this temperature range, a small heat capacity anomaly was detected and the negative magnetization effect took place in earlier reports. The wait-time dependence study of ZFC magnetization revealed an aging phenomenon. The frequency dependent peaks observed in the AC susceptibility and the aging phenomenon occurred below the Néel temperature might be indicative of the existence of a spin glass-like state in the present material at low temperatures.

  19. Self-focusing and self-compression of a laser pulse in the presence of an external tapered magnetized density-ramp plasma

    NASA Astrophysics Data System (ADS)

    Saedjalil, N.; Jafari, S.

    2016-06-01

    In this paper, the effects of external tapered axial magnetic field and plasma density-ramp on the spatiotemporal evolution of the laser pulse in inhomogeneous plasma have been studied. The external magnetic field can modify the refractive index of plasma and consequently intensifies the nonlinear effects. By considering the relativistic nonlinearity effect, self-focusing and self-compression of the laser beam propagating through the magnetized plasma have been investigated, numerically. Numerical results indicate that self-focusing and self-compression are better enhanced in a tapered magnetic field than in a uniform one. Besides, in plasma density-ramp profile, self-focusing and self-compression of the laser beam improve in comparison with no ramp structure. In addition, with increasing both the slope of the density ramp and slope constant parameter of the tapered magnetic field, the laser focusing increases, properly, in short distances of the laser propagation through the plasma.

  20. Dynamic magnetic hysteresis and nonlinear susceptibility of antiferromagnetic nanoparticles

    NASA Astrophysics Data System (ADS)

    Kalmykov, Yuri P.; Ouari, Bachir; Titov, Serguey V.

    2016-08-01

    The nonlinear ac stationary response of antiferromagnetic nanoparticles subjected to both external ac and dc fields of arbitrary strength and orientation is investigated using Brown's continuous diffusion model. The nonlinear complex susceptibility and dynamic magnetic hysteresis (DMH) loops of an individual antiferromagnetic nanoparticle are evaluated and compared with the linear regime for extensive ranges of the anisotropy, the ac and dc magnetic fields, damping, and the specific antiferromagnetic parameter. It is shown that the shape and area of the DMH loops of antiferromagnetic particles are substantially altered by applying a dc field that permits tuning of the specific magnetic power loss in the nanoparticles.

  1. Effect of obliqueness and external magnetic field on the characteristics of dust acoustic solitary waves in dusty plasma with two-temperature nonthermal ions

    NASA Astrophysics Data System (ADS)

    Sabetkar, Akbar; Dorranian, Davoud

    2015-03-01

    In this paper, a theoretical investigation has been made of obliquely propagating dust acoustic solitary wave (DASW) structures in a cold magnetized dusty plasma consisting of a negatively charged dust fluid, electrons, and two different types of nonthermal ions. The Zakharov-Kuznetsov (ZK) and modified Zakharov-Kuznetsov (MZK) equations, describing the small but finite amplitude DASWs, are derived using a reductive perturbation method. The combined effects of the external magnetic field, obliqueness (i.e. the propagation angle), and the presence of second component of nonthermal ions, which are found to significantly modify the basic features (viz. amplitude, width, polarity) of DASWs, are explicitly examined. The results show that the external magnetic field, the propagation angle, and the second component of nonthermal ions have strong effects on the properties of dust acoustic solitary structures. The solitary waves may become associated with either positive potential or negative potential in this model. As the angle between the direction of external magnetic field and the propagation direction of solitary wave increases, the amplitude of the solitary wave (for both positive potential and negative potential) increases. With changing this angle, the width of solitary wave shows a maximum. The magnitude of the external magnetic field has no direct effect on the solitary wave amplitude. However, with decreasing the strength of magnetic field, the width of DASW increases.

  2. Plasma filamentation and shock wave enhancement in microwave rockets by combining low-frequency microwaves with external magnetic field

    NASA Astrophysics Data System (ADS)

    Takahashi, Masayuki; Ohnishi, Naofumi

    2016-08-01

    A filamentary plasma is reproduced based on a fully kinetic model of electron and ion transports coupled with electromagnetic wave propagation. The discharge plasma transits from discrete to diffusive patterns at a 110-GHz breakdown, with decrease in the ambient pressure, because of the rapid electron diffusion that occurs during an increase in the propagation speed of the ionization front. A discrete plasma is obtained at low pressures when a low-frequency microwave is irradiated because the ionization process becomes more dominant than the electron diffusion, when the electrons are effectively heated by the low-frequency microwave. The propagation speed of the plasma increases with decrease in the incident microwave frequency because of the higher ionization frequency and faster plasma diffusion resulting from the increase in the energy-absorption rate. An external magnetic field is applied to the breakdown volume, which induces plasma filamentation at lower pressures because the electron diffusion is suppressed by the magnetic field. The thrust performance of a microwave rocket is improved by the magnetic fields corresponding to the electron cyclotron resonance (ECR) and its higher-harmonic heating, because slower propagation of the ionization front and larger energy-absorption rates are obtained at lower pressures. It would be advantageous if the fundamental mode of ECR heating is coupled with a lower frequency microwave instead of combining the higher-harmonic ECR heating with the higher frequency microwave. This can improve the thrust performance with smaller magnetic fields even if the propagation speed increases because of the decrease in the incident microwave frequency.

  3. Magnetic reconnection in the presence of externally driven and self-generated turbulence

    SciTech Connect

    Karimabadi, H.; Lazarian, A.

    2013-11-15

    Magnetic reconnection is an important process that violates flux freezing and induces change of magnetic field topology in conducting fluids and, as a consequence, converts magnetic field energy into particle energy. It is thought to be operative in laboratory, heliophysical, and astrophysical plasmas. These environments exhibit wide variations in collisionality, ranging from collisionless in the Earth's magnetosphere to highly collisional in molecular clouds. A common feature among these plasmas is, however, the presence of turbulence. We review the present understanding of the effects of turbulence on the reconnection rate, discussing both how strong pre-existing turbulence modifies Sweet-Parker reconnection and how turbulence may develop as a result of reconnection itself. In steady state, reconnection rate is proportional to the aspect ratio of the diffusion region. Thus, two general MHD classes of models for fast reconnection have been proposed, differing on whether they keep the aspect ratio finite by increasing the width due to turbulent broadening or shortening the length of the diffusion layer due to plasmoid instability. One of the consequences of the plasmoid instability model is the possibility that the current sheet thins down to collisionless scales where kinetic effects become dominant. As a result, kinetic effects may be of importance for many astrophysical applications which were considered to be in the realm of MHD. Whether pre-existing turbulence can significantly modify the transition to the kinetic regime is not currently known. Although most studies of turbulent reconnection have been based on MHD, recent advances in kinetic simulations are enabling 3D studies of turbulence and reconnection in the collisionless regime. A summary of these recent works, highlighting similarities and differences with the MHD models of turbulent reconnection, as well as comparison with in situ observations in the magnetosphere and in the solar wind, are presented

  4. Capture and separation of biomolecules using magnetic beads in a simple microfluidic channel without an external flow device.

    PubMed

    Wang, Jingjing; Morabito, Kenneth; Erkers, Tom; Tripathi, Anubhav

    2013-11-01

    The use of microfluidic devices and magnetic beads for applications in biotechnology has been extensively explored over the past decade. Many elaborate microfluidic chips have been used in efficient systems for biological assays. However most fail to achieve the ideal point of care (POC) status, as they require larger conventional external devices in conjunction with the microchip. This paper presents a simple technique to capture and separate biomolecules using magnetic bead movement on a microchip without the use of an external flow device. This microchip consisted of two well reservoirs (W1 and W2) connected via a tapered microchannel. Beads were dragged through the microchannel between the two wells at an equivalent speed to a permanent magnet that moved alongside the microchip. More than 95% of beads were transferred from W1 to W2 within 2 min at an average velocity of 0.7 mm s(-1). Enzymatic reactions were employed to test our microchip. Specifically, three assays were performed using the streptavidin coated magnetic beads as a solid support to capture and transfer biomolecules: (1) non-specific adsorption of the substrate, 6-8-difluoro-4-methylumbelliferyl phosphate (DiFMUP), (2) capture of the enzyme, biotinylated alkaline phosphatase (AP), and (3) separation of AP from DiFMUP. Our non-specific adsorption assay indicated that the microchip was capable of transferring the beads with less than 0.002% carryover of DiFMUP. Our capture assay indicated efficient capture and transfer of AP with beads to W2 containing DiFMUP, where the transferred AP converted 100% of DiFMUP to DiFMU within 15 minutes. Our separation assay showed effective separation of AP from DiFMUP and elucidated the binding capacity of the beads for AP. The leftover unbound AP in W1 converted 100% of DiFMUP within 10 minutes and samples with less than the full bead capacity of AP (i.e. all AP was transferred) did not convert any of the DiFMUP. The immobilization of AP on the bead surface

  5. Studying internal and external magnetic fields in Japan using MAGSAT data

    NASA Technical Reports Server (NTRS)

    Fukushima, N. (Principal Investigator); Maeda, H.; Yukutake, T.; Tanaka, M.; Oshima, S.; Ogawa, K.; Kawamura, M.; Miyazaki, Y.; Uyeda, S.; Kobayashi, K.

    1980-01-01

    Examination of the total intensity data of CHRONIT on a few paths over Japan and its neighboring sea shows MAGSAT is extremely useful for studying the local magnetic anomaly. In high latitudes, the signatures of field aligned currents are clearly recognized. These include (1) the persistent basic pattern of current flow; (2) the more intense currents in the summer hemisphere than in the winter hemisphere; (3) more fluctuations in current intensities in summer dawn hours; and (4) apparent dawn-dusk asymmetry in the field-aligned current intensity between the north and south polar regions.

  6. Electron energy boosting in laser-wake-field acceleration with external magnetic field Bapprox1 T and laser prepulses

    SciTech Connect

    Hosokai, Tomonao; Zhidkov, Alexei; Yamazaki, Atsushi; Mizuta, Yoshio; Uesaka, Mitsuru; Kodama, Ryosuke

    2010-03-22

    Hundred-mega-electron-volt electron beams with quasi-monoenergetic distribution, and a transverse geometrical emittance as small as approx0.02 pi mm mrad are generated by low power (7 TW, 45 fs) laser pulses tightly focused in helium gas jets in an external static magnetic field, Bapprox1 T. Generation of monoenergetic beams strongly correlates with appearance of a straight, at least 2 mm length plasma channel in a short time before the main laser pulse and with the energy of copropagating picosecond pedestal pulses (PPP). For a moderate energy PPP, the multiple or staged electron self-injection in the channel gives several narrow peaks in the electron energy distribution.

  7. Amplification of acoustic waves in armchair graphene nanoribbon in the presence of external electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Dompreh, K. A.; Mensah, S. Y.; Abukari, S. S.; Sam, F.; Mensah, N. G.

    2016-09-01

    Amplification of acoustic waves in Armchair Graphene Nanoribbon (AGNR) in the presence of an external electric and magnetic fields was studied using the Boltzmann's kinetic equation. The general expression for the amplification (Γ⊥ /Γ0) was obtained in the region ql ≫ 1 for the energy dispersion ε(p →) near the Fermi point. For various parameters of the quantized wave vector (β), the graphs of Γ⊥ /Γ0 against the electric field (Ex →), the acoustic wave-number (q →), the energy gap (Eg) and the dimensionless factor (Ωτ0) were numerically analyzed. The results showed a linear relation for Γ⊥ /Γ0 with Ex → but non-linear for q → and Ωτ0. The observed amplification can lead to SASER in Armchair Graphene Nanoribbon (AGNR).

  8. Control of wake and vortex shedding behind a porous circular obstacle by exerting an external magnetic field

    NASA Astrophysics Data System (ADS)

    Bovand, M.; Rashidi, S.; Dehghan, M.; Esfahani, J. A.; Valipour, M. S.

    2015-07-01

    In this article the finite volume method (FVM) is carried out to simulate the flow around and through a two-dimensional porous cylinder. An external magnetic field is used to control the wake behind the bluff body and also to suppress the vortex shedding phenomena. The Darcy-Brinkman-Forchheimer model has been used for modeling the flow in the porous medium. Effects of Stuart (N), Reynolds (Re) and Darcy (Da) numbers on the flow behavior have been investigated. The results show that the critical Stuart number for suppress vortex shedding decreases with increasing the Darcy numbers. Also, the Stuart number for disappearance the re-circulating wake increases with increased Reynolds number for both porous and solid cylinders.

  9. Tearing mode dynamics and locking in the presence of external magnetic perturbations

    NASA Astrophysics Data System (ADS)

    Fridström, R.; Munaretto, S.; Frassinetti, L.; Chapman, B. E.; Brunsell, P. R.; Sarff, J. S.

    2016-06-01

    In normal operation, Madison Symmetric Torus (MST) [R. N. Dexter et al., Fusion Technol. 19, 131 (1991)] reversed-field pinch plasmas exhibit several rotating tearing modes (TMs). Application of a resonant magnetic perturbation (RMP) results in braking of mode rotation and, if the perturbation amplitude is sufficiently high, in a wall-locked state. The coils that produce the magnetic perturbation in MST give rise to RMPs with several toroidal harmonics. As a result, simultaneous deceleration of all modes is observed. The measured TM dynamics is shown to be in qualitative agreement with a magnetohydrodynamical model of the RMP interaction with the TM [R. Fitzpatrick, Nucl. Fusion 33, 1049 (1993)] adapted to MST. To correctly model the TM dynamics, the electromagnetic torque acting on several TMs is included. Quantitative agreement of the TM slowing-down time was obtained for a kinematic viscosity in the order of νki n≈10 -20 m2/s. Analysis of discharges with different plasma densities shows an increase of the locking threshold with increasing density. Modeling results show good agreement with the experimental trend, assuming a density-independent kinematic viscosity. Comparison of the viscosity estimates in this paper to those made previously with other techniques in MST plasmas suggests the possibility that the RMP technique may allow for estimates of the viscosity over a broad range of plasmas in MST and other devices.

  10. Tevatron AC dipole system

    SciTech Connect

    Miyamoto, R.; Kopp, S.E.; Jansson, A.; Syphers, M.J.; /Fermilab

    2007-06-01

    The AC dipole is an oscillating dipole magnet which can induce large amplitude oscillations without the emittance growth and decoherence. These properties make it a good tool to measure optics of a hadron synchrotron. The vertical AC dipole for the Tevatron is powered by an inexpensive high power audio amplifier since its operating frequency is approximately 20 kHz. The magnet is incorporated into a parallel resonant system to maximize the current. The use of a vertical pinger magnet which has been installed in the Tevatron made the cost relatively inexpensive. Recently, the initial system was upgraded with a more powerful amplifier and oscillation amplitudes up to 2-3{sigma} were achieved with the 980 GeV proton beam. This paper discusses details of the Tevatron AC dipole system and also shows its test results.

  11. Ion exchange kinetics of magnetic alginate ferrogel beads produced by external gelation.

    PubMed

    Teixeira, Vânea Ferreira Torres; Pereira, Nádia Rosa; Waldman, Walter Ruggeri; Ávila, Ana Luiza Cassiano Dias; Pérez, Victor Haber; Rodríguez, Rubén Jesus Sánchez

    2014-10-13

    This paper reports on a study of the influence of sodium alginate concentration and iron addition on the ion exchange kinetics of calcium alginate ferrogel beads produced by external gelation. The calcium absorption and sodium release of the beads were fitted to Fick's second law for unsteady state diffusion in order to obtain the effective diffusion coefficients of Na(+) and Ca(2+). The dried beads were characterized concerning their thermal stability, particle size distribution and morphology. The gelation kinetics showed that an increase in alginate concentration from 1% to 2% increased the Ca(2+) equilibrium concentration, but presented no effect on Ca(2+) effective diffusion coefficient. Alginate concentration higher than 2% promoted saturation of binding sites at the bead surfaces. The addition of iron promoted faster diffusion of Ca(2+) inside the gel beads and reduced the Ca(2+) equilibrium concentration. Also, iron particles entrapped in the alginate gel beads promoted greater absorption of water compared to pure alginate gel and lower thermal stability of the beads. The main diffusion of Ca(2+) into and Na(+) out from the bead took place during the first 60 min, during which almost 85-90% of the Ca(2+) equilibrium concentration is achieved, indicating that this period is sufficient to produce a Ca-alginate bead with high crosslinking of the polymer network. PMID:25037343

  12. The effect of external magnetic field on the density distributions and electromagnetic fields in the interaction of high-intensity short laser pulse with collisionless underdense plasma

    NASA Astrophysics Data System (ADS)

    Mahmoodi-Darian, Masoomeh; Ettehadi-Abari, Mehdi; Sedaghat, Mahsa

    2016-03-01

    Laser absorption in the interaction between ultra-intense femtosecond laser and solid density plasma is studied theoretically here in the intensity range I{λ^2} ˜eq 10^{14}{-}10^{16}{{W}}{{{cm}}^{-2}} \\upmu{{{m}}2} . The collisionless effect is found to be significant when the incident laser intensity is less than 10^{16}{{W}}{{{cm}}^{-2}}\\upmu{{{m}}2} . In the current work, the propagation of a high-frequency electromagnetic wave, for underdense collisionless plasma in the presence of an external magnetic field is investigated. When a constant magnetic field parallel to the laser pulse propagation direction is applied, the electrons rotate along the magnetic field lines and generate the electromagnetic part in the wake with a nonzero group velocity. Here, by considering the ponderomotive force in attendance of the external magnetic field and assuming the isothermal collisionless plasma, the nonlinear permittivity of the plasma medium is obtained and the equation of electromagnetic wave propagation in plasma is solved. Here, by considering the effect of the ponderomotive force in isothermal collisionless magnetized plasma, it is shown that by increasing the laser pulse intensity, the electrons density profile leads to steepening and the electron bunches of plasma become narrower. Moreover, it is found that the wavelength of electric and magnetic field oscillations increases by increasing the external magnetic field and the density distribution of electrons also grows in comparison to the unmagnetized collisionless plasma.

  13. Quasilongitudinal soliton in a two-dimensional strongly coupled complex dusty plasma in the presence of an external magnetic field.

    PubMed

    Ghosh, Samiran

    2014-09-01

    The propagation of a nonlinear low-frequency mode in two-dimensional (2D) monolayer hexagonal dusty plasma crystal in presence of external magnetic field and dust-neutral collision is investigated. The standard perturbative approach leads to a 2D Korteweg-de Vries (KdV) soliton for the well-known dust-lattice mode. However, the Coriolis force due to crystal rotation and Lorentz force due to magnetic field on dust particles introduce a linear forcing term, whereas dust-neutral drag introduce the usual damping term in the 2D KdV equation. This new nonlinear equation is solved both analytically and numerically to show the competition between the linear forcing and damping in the formation of quasilongitudinal soliton in a 2D strongly coupled complex (dusty) plasma. Numerical simulation on the basis of the typical experimental plasma parameters and the analytical solution reveal that the neutral drag force is responsible for the usual exponential decay of the soliton, whereas Coriolis and/or Lorentz force is responsible for the algebraic decay as well as the oscillating tail formation of the soliton. The results are discussed in the context of the plasma crystal experiment. PMID:25314548

  14. Research of transportation efficiency of low-energy high- current electron beam in plasma channel in external magnetic field

    NASA Astrophysics Data System (ADS)

    Vagin, E. S.; Grigoriev, V. P.

    2015-11-01

    Effective high current (5-20 kA) and low energy (tens of keV) electrons beam transportation is possible only with almost complete charging neutralization. It is also necessary to use quite high current neutralization for elimination beam self-pinching effect. The research is based on the self-consistent mathematical model that takes into account beam and plasma particles dynamic, current and charge neutralization of electron beam and examines the transportation of electron beam into a chamber with low-pressure plasma in magnetic field. A numerical study was conducted using particle in cell (PIC) method. The study was performed with various system parameters: rise time and magnitude of the beam current, gas pressure and plasma density and geometry of the system. Regularities of local virtual cathode field generated by the beam in the plasma channel, as well as ranges of parameters that let transportation beam with minimal losses, depending on the external magnetic field were determined through a series of numerical studies. In addition, the assessment of the impact of the plasma ion mobility during the transition period and during steady beam was performed.

  15. Evaluation of the toroidal torque driven by external non-resonant non-axisymmetric magnetic field perturbations in a tokamak

    NASA Astrophysics Data System (ADS)

    Kasilov, Sergei V.; Kernbichler, Winfried; Martitsch, Andreas F.; Maassberg, Henning; Heyn, Martin F.

    2014-09-01

    The toroidal torque driven by external non-resonant magnetic perturbations (neoclassical toroidal viscosity) is an important momentum source affecting the toroidal plasma rotation in tokamaks. The well-known force-flux relation directly links this torque to the non-ambipolar neoclassical particle fluxes arising due to the violation of the toroidal symmetry of the magnetic field. Here, a quasilinear approach for the numerical computation of these fluxes is described, which reduces the dimension of a standard neoclassical transport problem by one without model simplifications of the linearized drift kinetic equation. The only limiting condition is that the non-axisymmetric perturbation field is small enough such that the effect of the perturbation field on particle motion within the flux surface is negligible. Therefore, in addition to most of the transport regimes described by the banana (bounce averaged) kinetic equation also such regimes as, e.g., ripple-plateau and resonant diffusion regimes are naturally included in this approach. Based on this approach, a quasilinear version of the code NEO-2 [W. Kernbichler et al., Plasma Fusion Res. 3, S1061 (2008).] has been developed and benchmarked against a few analytical and numerical models. Results from NEO-2 stay in good agreement with results from these models in their pertinent range of validity.

  16. Evaluation of the toroidal torque driven by external non-resonant non-axisymmetric magnetic field perturbations in a tokamak

    SciTech Connect

    Kasilov, Sergei V.; Kernbichler, Winfried; Martitsch, Andreas F.; Heyn, Martin F.; Maassberg, Henning

    2014-09-15

    The toroidal torque driven by external non-resonant magnetic perturbations (neoclassical toroidal viscosity) is an important momentum source affecting the toroidal plasma rotation in tokamaks. The well-known force-flux relation directly links this torque to the non-ambipolar neoclassical particle fluxes arising due to the violation of the toroidal symmetry of the magnetic field. Here, a quasilinear approach for the numerical computation of these fluxes is described, which reduces the dimension of a standard neoclassical transport problem by one without model simplifications of the linearized drift kinetic equation. The only limiting condition is that the non-axisymmetric perturbation field is small enough such that the effect of the perturbation field on particle motion within the flux surface is negligible. Therefore, in addition to most of the transport regimes described by the banana (bounce averaged) kinetic equation also such regimes as, e.g., ripple-plateau and resonant diffusion regimes are naturally included in this approach. Based on this approach, a quasilinear version of the code NEO-2 [W. Kernbichler et al., Plasma Fusion Res. 3, S1061 (2008).] has been developed and benchmarked against a few analytical and numerical models. Results from NEO-2 stay in good agreement with results from these models in their pertinent range of validity.

  17. Templating Biomineralization: Surface Directed Protein Self-assembly and External Magnetic Field Stimulation of Osteoblasts

    NASA Astrophysics Data System (ADS)

    Ba, Xiaolan

    Biomineralization is a wide-spread phenomenon in the biological systems, which is the process of mineral formation by organisms through interaction between its organic contents and the inorganic minerals. The process is essential in a broad spectrum of biological phenomena ranging from bone and tooth formation to pathological mineralization under hypoxic conditions or cancerous formations. In this thesis I studied biomineralization at the earliest stages in order to obtain a better understanding of the fundamental principals involved. This knowledge is essential if we want to engineer devices which will increase bone regeneration or prevent unwanted mineral deposits. Extracellular matrix (ECM) proteins play an essential role during biomineralization in bone and engineered tissues. In this dissertation, I present an approach to mimic the ECM in vitro to probe the interactions of these proteins with calcium phosphate mineral and with each other. Early stage of mineralization is investigated by mechanical properties of the protein fibers using Scanning Probe Microscopy (SPM) and Shear Modulation Force Microscopy (SMFM). The development of mineral crystals on the protein matrices is also characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Grazing Incidence X-ray Diffraction (GIXRD). The results demonstrate complementary actions of the two ECM proteins to collect cations and template calcium phosphate mineral, respectively. Magnets have been clinically used as an "induction source" in various bone or orthodontic treatments. However, the mechanism and effects of magnetic fields remain unclear. In this dissertation, I also undertake the present investigation to study the effects of 150 mT static magnetic fields (SMF) on ECM development and cell biomineralization using MC3T3-E1 osteobalst-like cells. Early stage of biomineralization is characterized by SPM, SMFM and confocal laser scanning microscopy (CSLM). Late stage of

  18. Influence of external magnetic field on thermophysical parameters of magnetic fluid based on aqueous hydrogen peroxide or ethylene glycol with a mixture of lanthanum manganite powder and toner printer cartridge

    NASA Astrophysics Data System (ADS)

    Zaripov, Jamshed; Borisov, Boris

    2014-08-01

    Heat transfer agent magnetic fluids based on aqueous solutions of hydrogen peroxide or a mixture of ethylene glycol with the powders of lanthanum manganite and the toner cartridge are considered. Experimental data on the effect produced by an external magnetic field on the characteristics of magnetic fluids and heat exchanger efficiency were analyzed. As the heat exchanger is considered flat-plate solar collector. The conclusion about the possibility of using the above technologies to improve the efficiency of heat exchangers.

  19. Pretreatment Endorectal Magnetic Resonance Imaging and Magnetic Resonance Spectroscopic Imaging Features of Prostate Cancer as Predictors of Response to External Beam Radiotherapy

    SciTech Connect

    Joseph, Tim; McKenna, David A.; Westphalen, Antonio C.; Coakley, Fergus V. Zhao Shoujun; Lu Ying; Hsu, I.-C.; Roach, Mack; Kurhanewicz, John

    2009-03-01

    Purpose: To evaluate whether pretreatment combined endorectal magnetic resonance imaging (MRI) and magnetic resonance spectroscopic imaging (MRSI) findings are predictive of outcome in patients who undergo external beam radiotherapy for prostate cancer. Methods and Materials: We retrospectively identified 67 men with biopsy-proven prostate cancer who underwent combined endorectal MRI and MRSI at our institution between January 1998 and October 2003 before whole-pelvis external beam radiotherapy. A single reader recorded tumor presence, stage, and metabolic abnormality at combined MRI and MRSI. Kaplan-Meier survival and Cox univariate and multivariate analyses explored the relationship between clinical and imaging variables and outcome, using biochemical or metastatic failure as endpoints. Results: After a mean follow-up of 44 months (range, 3-96), 6 patients developed both metastatic and biochemical failure, with an additional 13 patients developing biochemical failure alone. Multivariate Cox analysis demonstrated that the only independent predictor of biochemical failure was the volume of malignant metabolism on MRSI (hazard ratio [HR] 1.63, 95% confidence interval [CI] 1.29-2.06; p < 0.0001). The two independent predictors of metastatic failure were MRI tumor size (HR 1.34, 95% CI 1.03-1.73; p = 0.028) and the finding of seminal vesicle invasion on MRI (HR 28.05, 95% CI 3.96-198.67; p = 0.0008). Conclusions: In multivariate analysis, MRI and MRSI findings before EBRT in patients with prostate cancer are more accurate independent predictors of outcome than clinical variables, and in particular, the findings of seminal vesicle invasion and extensive tumor predict a worse prognosis.

  20. Increased cellular uptake of biocompatible superparamagnetic iron oxide nanoparticles into malignant cells by an external magnetic field.

    PubMed

    Prijic, Sara; Scancar, Janez; Romih, Rok; Cemazar, Maja; Bregar, Vladimir B; Znidarsic, Andrej; Sersa, Gregor

    2010-07-01

    Superparamagnetic iron oxide nanoparticles (SPIONs) are used as delivery systems for different therapeutics including nucleic acids for magnetofection-mediated gene therapy. The aim of our study was to evaluate physicochemical properties, biocompatibility, cellular uptake and trafficking pathways of the custom-synthesized SPIONs for their potential use in magnetofection. Custom-synthesized SPIONs were tested for size, shape, crystalline composition and magnetic behavior using a transmission electron microscope, X-ray diffractometer and magnetometer. SPIONs were dispersed in different aqueous media to obtain ferrofluids, which were tested for pH and stability using a pH meter and zetameter. Cytotoxicity was determined using the MTS and clonogenic assays. Cellular uptake and trafficking pathways were qualitatively evaluated by transmission electron microscopy and quantitatively by inductively coupled plasma atomic emission spectrometry. SPIONs were composed of an iron oxide core with a diameter of 8-9 nm, coated with a 2-nm-thick layer of silica. SPIONs, dispersed in 0.9% NaCl solution, resulted in a stable ferrofluid at physiological pH for several months. SPIONs were not cytotoxic in a broad range of concentrations and were readily internalized into different cells by endocytosis. Exposure to neodymium-iron-boron magnets significantly increased the cellular uptake of SPIONs, predominantly into malignant cells. The prepared SPIONs displayed adequate physicochemical and biomedical properties for potential use in magnetofection. Their cellular uptake was dependent on the cell type, and their accumulation within the cells was dependent on the duration of exposure to an external magnetic field. PMID:20602230

  1. Increased Cellular Uptake of Biocompatible Superparamagnetic Iron Oxide Nanoparticles into Malignant Cells by an External Magnetic Field

    PubMed Central

    Prijic, Sara; Scancar, Janez; Romih, Rok; Cemazar, Maja; Bregar, Vladimir B.; Znidarsic, Andrej

    2010-01-01

    Superparamagnetic iron oxide nanoparticles (SPIONs) are used as delivery systems for different therapeutics including nucleic acids for magnetofection-mediated gene therapy. The aim of our study was to evaluate physicochemical properties, biocompatibility, cellular uptake and trafficking pathways of the custom-synthesized SPIONs for their potential use in magnetofection. Custom-synthesized SPIONs were tested for size, shape, crystalline composition and magnetic behavior using a transmission electron microscope, X-ray diffractometer and magnetometer. SPIONs were dispersed in different aqueous media to obtain ferrofluids, which were tested for pH and stability using a pH meter and zetameter. Cytotoxicity was determined using the MTS and clonogenic assays. Cellular uptake and trafficking pathways were qualitatively evaluated by transmission electron microscopy and quantitatively by inductively coupled plasma atomic emission spectrometry. SPIONs were composed of an iron oxide core with a diameter of 8–9 nm, coated with a 2-nm-thick layer of silica. SPIONs, dispersed in 0.9% NaCl solution, resulted in a stable ferrofluid at physiological pH for several months. SPIONs were not cytotoxic in a broad range of concentrations and were readily internalized into different cells by endocytosis. Exposure to neodymium-iron-boron magnets significantly increased the cellular uptake of SPIONs, predominantly into malignant cells. The prepared SPIONs displayed adequate physicochemical and biomedical properties for potential use in magnetofection. Their cellular uptake was dependent on the cell type, and their accumulation within the cells was dependent on the duration of exposure to an external magnetic field. PMID:20602230

  2. Formation and ultraslow propagation of infrared solitons in graphene under an external magnetic field

    SciTech Connect

    Ding, Chunling; Yu, Rong; Hao, Xiangying; Li, Jiahua E-mail: yingwu2@126.com; Wu, Ying E-mail: yingwu2@126.com

    2014-06-21

    Unusual dispersion relation of graphene nanoribbons for electrons can lead to an exceptionally strong optical response in the infrared regime and exhibits a very good tunable frequency. According to quantum optics and solid-material scientific principles, here we show the possibility to generate ultraslow infrared bright and dark solitons in graphene under the action of strong magnetic and infrared laser fields. By means of quantum-mechanical density-matrix formalism, we derive the equations of motion that govern the nonlinear evolution of the probe-pulse envelope in this scheme. It is found that, by properly choosing the parameters of the system, the formation and ultraslow propagation of infrared spatial solitons originate from the balance between nonlinear effects and the dispersion properties of the graphene under infrared excitation. Moreover, the unique electronic properties and selection rules near the Dirac point provide more freedom for us to study the linear and nonlinear dynamical responses of the photonics and graphene system. These results may have potential applications in telecommunication and optical information processing.

  3. Formation and ultraslow propagation of infrared solitons in graphene under an external magnetic field

    NASA Astrophysics Data System (ADS)

    Ding, Chunling; Yu, Rong; Li, Jiahua; Hao, Xiangying; Wu, Ying

    2014-06-01

    Unusual dispersion relation of graphene nanoribbons for electrons can lead to an exceptionally strong optical response in the infrared regime and exhibits a very good tunable frequency. According to quantum optics and solid-material scientific principles, here we show the possibility to generate ultraslow infrared bright and dark solitons in graphene under the action of strong magnetic and infrared laser fields. By means of quantum-mechanical density-matrix formalism, we derive the equations of motion that govern the nonlinear evolution of the probe-pulse envelope in this scheme. It is found that, by properly choosing the parameters of the system, the formation and ultraslow propagation of infrared spatial solitons originate from the balance between nonlinear effects and the dispersion properties of the graphene under infrared excitation. Moreover, the unique electronic properties and selection rules near the Dirac point provide more freedom for us to study the linear and nonlinear dynamical responses of the photonics and graphene system. These results may have potential applications in telecommunication and optical information processing.

  4. Demountable externally anchored low-stress magnet system and related method

    DOEpatents

    Powell, James; Hsieh, Shih-Yung; Lehner, John R.

    1981-01-01

    Toroidal field coils are interlaced with other toroidal structures and are operated under supercooled conditions. To facilitate demounting the toroidal field coils, which are supercooled, they are made in the form of connected segments constituting coils of polygonal form. The segments may be rectilinear in form, but some may also be U-shaped or L-shaped. The segments are detachable from one another and are supported in load relieving manner. Power devices are used to displace the segments to facilitate removal of the coils from the aforesaid toroidal structures and to provide for the accommodation of dimensional changes and stresses due to thermal and magnetic conditions. The segments are formed of spaced parallel conductive slabs with the slabs of one segment being interdigitated with the slabs of the adjacent segment. The interdigitated slabs may be soldered together or slidingly engaged. The slabs are shaped to accommodate superconductors and to provide passages for a cooling medium. The slabs are moreover separated by insulator slabs with which they form a coil structure which is jacketed.

  5. Ac loss characteristics of YBCO superconducting tapes fabricated by TFA-MOD technique

    NASA Astrophysics Data System (ADS)

    Iwakuma, Masataka; Nigo, Masahiro; Inoue, Daisuke; Miyamoto, Naoya; Kiss, Takanobu; Funaki, Kazuo; Iijima, Yasuhiro; Saitoh, Takashi; Izumi, Teruo; Yamada, Yutaka; Shiohara, Yuu

    2005-10-01

    We investigated the ac loss properties of a YBCO superconducting tape fabricated by TFA-MOD technique. The thickness of the YBCO layer is 1.2 μm. A 6-tape stack of 50 mm in length and 10 mm in width was inserted into a saddle-shaped pickup coil. The ac loss was measured at 35-77 K by applying an external ac magnetic field. The magnetic field angle was changed by rotating the sample stack around its longitudinal axis. The effective penetration field, which corresponds to the breaking point of an ac loss curve, decreased with increasing field angle though it was much smaller than that which was estimated for a superconducting slab with the same thickness as the width of a tape. As a result, the ac loss increased monotonically with an increasing field angle against the wide surface for any amplitude. The observed field angular dependence of the ac loss agreed with the theoretically predicted one by using the observed ac losses in perpendicular magnetic field. Anyway the ac loss for a larger amplitude than the effective penetration field was proportional to the critical current density and the projective width of a tape in the direction of the applied magnetic field for any field angle and any temperature as well known. In addition we estimated the magnetic field, B, dependence of the critical current, Ic, from the observed magnetization curves. It was shown that zero-field Ic appeared to be a linear function of temperature and Ic-B characteristics was scaled with zero-field Ic. We also discussed a difference in Ic-B characteristics and its temperature dependence between TFA-MOD tapes and IBAD-PLD ones.

  6. The effect of external magnetic field on the bremsstrahlung nonlinear absorption mechanism in the interaction of high intensity short laser pulse with collisional underdense plasma

    SciTech Connect

    Sedaghat, M.; Ettehadi-Abari, M.; Shokri, B. Ghorbanalilu, M.

    2015-03-15

    Laser absorption in the interaction between ultra-intense femtosecond laser and solid density plasma is studied theoretically here in the intensity range Iλ{sup 2}≃10{sup 14}−10{sup 16}Wcm{sup −2}μm{sup 2}. The collisional effect is found to be significant when the incident laser intensity is less than 10{sup 16}Wcm{sup −2}μm{sup 2}. In the current work, the propagation of a high frequency electromagnetic wave, for underdense collisional plasma in the presence of an external magnetic field is investigated. It is shown that, by considering the effect of the ponderomotive force in collisional magnetized plasmas, the increase of laser pulse intensity leads to steepening of the electron density profile and the electron bunches of plasma makes narrower. Moreover, it is found that the wavelength of electric and magnetic fields oscillations increases by increasing the external magnetic field and the density distribution of electrons also grows in comparison with the unmagnetized collisional plasma. Furthermore, the spatial damping rate of laser energy and the nonlinear bremsstrahlung absorption coefficient are obtained in the collisional regime of magnetized plasma. The other remarkable result is that by increasing the external magnetic field in this case, the absorption coefficient increases strongly.

  7. Chaotic dynamics and basin erosion in nanomagnets subject to time-harmonic magnetic fields

    NASA Astrophysics Data System (ADS)

    d'Aquino, M.; Quercia, A.; Serpico, C.; Bertotti, G.; Mayergoyz, I. D.; Perna, S.; Ansalone, P.

    2016-04-01

    Magnetization dynamics in uniformly magnetized particles subject to time-harmonic (AC) external fields is considered. The study is focused on the behavior of the AC-driven dynamics close to saddle equilibria. It happens that such dynamics has chaotic nature at moderately low power level, due to the heteroclinic tangle phenomenon which is produced by the combined effect of AC-excitations and saddle type dynamics. By using analytical theory for the threshold AC excitation amplitudes necessary to create the heteroclinic tangle together with numerical simulations, we quantify and show how the tangle produces the erosion of the safe basin around the stable equilibria.

  8. Entanglement in a time-dependent coupled XY spin chain in an external magnetic field

    SciTech Connect

    Sadiek, Gehad; Alkurtass, Bedoor; Aldossary, Omar

    2010-11-15

    We consider an infinite one-dimensional anisotropic XY spin chain with a nearest-neighbor time-dependent Heisenberg coupling J(t) between the spins in presence of a time-dependent magnetic field h(t). We discuss a general solution for the system and present an exact solution for particular choice of J and h of practical interest. We investigate the dynamics of entanglement for different degrees of anisotropy of the system and at both zero and finite temperatures. We find that the time evolution of entanglement in the system shows nonergodic and critical behavior at zero and finite temperatures and different degrees of anisotropy. The asymptotic behavior of entanglement at the infinite time limit at zero temperature and constant J and h depends only the parameter {lambda}=J/h rather than the individual values of J and h for all degrees of anisotropy but changes for nonzero temperature. Furthermore, the asymptotic behavior is very sensitive to the initial values of J and h and for particular choices we may create finite asymptotic entanglement regardless of the final values of J and h. The persistence of quantum effects in the system as it evolves and as the temperature is raised is studied by monitoring the entanglement. We find that the quantum effects dominate within certain regions of the kT-{lambda} space that vary significantly depending on the degree of the anisotropy of the system. Particularly, the quantum effects in the Ising model case persist in the vicinity of both its critical phase transition point and zero temperature as it evolves in time. Moreover, the interplay between the different system parameters to tune and control the entanglement evolution is explored.

  9. Entanglement in a time-dependent coupled XY spin chain in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Sadiek, Gehad; Alkurtass, Bedoor; Aldossary, Omar

    2010-11-01

    We consider an infinite one-dimensional anisotropic XY spin chain with a nearest-neighbor time-dependent Heisenberg coupling J(t) between the spins in presence of a time-dependent magnetic field h(t). We discuss a general solution for the system and present an exact solution for particular choice of J and h of practical interest. We investigate the dynamics of entanglement for different degrees of anisotropy of the system and at both zero and finite temperatures. We find that the time evolution of entanglement in the system shows nonergodic and critical behavior at zero and finite temperatures and different degrees of anisotropy. The asymptotic behavior of entanglement at the infinite time limit at zero temperature and constant J and h depends only the parameter λ=J/h rather than the individual values of J and h for all degrees of anisotropy but changes for nonzero temperature. Furthermore, the asymptotic behavior is very sensitive to the initial values of J and h and for particular choices we may create finite asymptotic entanglement regardless of the final values of J and h. The persistence of quantum effects in the system as it evolves and as the temperature is raised is studied by monitoring the entanglement. We find that the quantum effects dominate within certain regions of the kT-λ space that vary significantly depending on the degree of the anisotropy of the system. Particularly, the quantum effects in the Ising model case persist in the vicinity of both its critical phase transition point and zero temperature as it evolves in time. Moreover, the interplay between the different system parameters to tune and control the entanglement evolution is explored.

  10. A linear magnetic motor and generator

    NASA Technical Reports Server (NTRS)

    Studer, P. A.

    1980-01-01

    In linear magnetic motor and generator suitable for remote and hostile environments, magnetic forces drive reciprocating shaft along its axis. Actuator shaft is located in center of cylindrical body and may be supported by either contacting or noncontacting bearings. When device operates as bidirectional motor, drive coil selectively adds and subtracts magnetic flux to and from flux paths, producing forces that drive actuator along axis. When actuator is driven by external reciprocating engine, device becomes ac generator.

  11. Fighting cancer with magnetic nanoparticles and immunotherapy

    NASA Astrophysics Data System (ADS)

    Gutiérrez, L.; Mejías, R.; Barber, D. F.; Veintemillas-Verdaguer, S.; Serna, C. J.; Lázaro, F. J.; Morales, M. P.

    2012-03-01

    IFN-γ-adsorbed DMSA-coated magnetite nanoparticles can be used as an efficient in vivo drug delivery system for tumor immunotherapy. Magnetic nanoparticles, with adsorbed interferon-γ, were targeted to the tumor site by application of an external magnetic field. A relevant therapeutic dosage of interferon in the tumor was detected and led to a notable reduction in tumor size. In general, only 10% of the total injected nanoparticles after multiple exposures were found in tissues by AC susceptibility measurements of the corresponding resected tissues. Magnetic nanoparticle biodistribution is affected by the application of an external magnetic field.

  12. The use of field dependence of AC susceptibility for the interpretation of magnetic mineralogy and magnetic fabrics in the HSDP-2 basalts, Hawaii [rapid communication

    NASA Astrophysics Data System (ADS)

    Vahle, Carsten; Kontny, Agnes

    2005-09-01

    We applied the field dependence parameter χHd (%) = [( k300A/m - k30A/m) / k300A/m] × 100 given by de Wall for the subaerial and submarine basalts drilled by the 3109 m deep HSDP-2 borehole on Hawaii in order to verify the hypothesis that mainly composition controls the field dependence of AC susceptibility in titanomagnetite of natural occurrences. When we used this parameter, our data showed a significant scattering compared to data presented in earlier studies. In addition to composition, the effect of measurement temperature, grain size and anisotropy on the field dependent susceptibility were examined and found to be critical. The impact of grain size is weaker than the other effects. It cannot be totally excluded that the observed effects arise indirectly through an overlap of the other effects for the investigated basalts. The most important factor for the variation of field dependence is the degree of oxidation, causing a modification of the titanomagnetite composition or formation of titanomaghemite, and the mixing of Ti-rich with Ti-poor titanomagnetites, which strongly reduces the χHd parameter. Field dependence is not only related to titanomagnetite composition, especially for intermediate titanomagnetites with TCs between 100 and 300 °C. Temperature dependent susceptibility measurements at different field amplitudes for these intermediate types showed at constant geometry of the k( T) curve great differences in susceptibility, resulting in significant changes of the field dependence parameter over the temperature interval from - 100 to 260 °C. Therefore variations of the ambient measurement temperatures are able to influence the field dependence. The second important effect is the degree of particle shape and alignment, which controls the field dependence in different orientations especially for the intermediate titanomagnetite, which is intensively intergrown with elongated hemoilmenite grains. As a consequence, samples with higher degrees of

  13. Hysteretic Dependence of Magnetic Flux Density on Primary AC Current in Flat-Type Inductive Fault Current Limiter with YBCO Thin Film Discs

    NASA Astrophysics Data System (ADS)

    Harada, Masayuki; Yokomizu, Yasunobu; Matsumura, Toshiro

    2014-05-01

    This paper focuses on a flat-type inductive superconducting FCL (FIS-FCL) consisting of a pancake coil and a YBCO thin layer disc. AC current injection experiments and magnetic field analysis were carried out for two kinds of FIS-FCL, single-disc model and double-discs model. In the former, the pancake coil was putted on the YBCO disc. In the latter, the pancake coil was sandwiched with two YBCO discs. The double-discs model cancels out the magnetic flux density more effectively than the single-disc model. In the double-discs model, the superconducting state period is longer than in the single-disc model. Thus, it may be concluded that the double-discs model is considered to be suitable for FIS-FCL.

  14. Abstract: Magnetic solitons' contribution to the specific heat of (CH3)4NMnCl3 in an external magnetic field

    NASA Astrophysics Data System (ADS)

    Borsa, F.

    1982-03-01

    It has been shown theoretically that linear magnetic systems with planar anisotropy should display nonlinear excitations, i.e., sine-Gordon solitons upon application of a magnetic field perpendicular to the chain axis. Experimental evidence for ID magnetic solitons has been presented for TMMC from neutron scattering and NMR measurements.1 The classical statistical mechanics of this system predict a soliton contribution to the free energy and thus to the specific heat.2 In order to test experimentally the thermodynamic relevance of magnetic solitons, I performed measurements of specific heat in single crystal TMMC in an external magnetic field up to 10 Tesla, applied both perpendicular and parallel to the chain. The measurements were performed with an adiabatic calorimeter in the temperature range 1.5-15 °K. The results show an extra contribution for H⊥c not present for H∥c. This contribution displays a broad maximum which scales approximately as H/T in agreement with the theory. The maximum occurs just above the peak in the specific heat which is observed in correspondence to the three-dimensional transition temperature, and it can be clearly resolved only for H⩾5.0 T. The soliton energy obtained by fitting the experiments to the classical theory is Es = 2.0 H for H = 5.39 T and Es = 1.8 H for H = 10 T to be compared with the theoretical value of Es = gμBHS = 3.35 H and with the value obtained by neutron scattering at H = 3.2 T, i.e., Es = 2.6 H. The discrepancy between theory and experiment is discussed in terms of renormalization corrections and of a possible soliton instability occurring for fields between 3 and 5 T. a)Permanent address: Institut di Fisica, Universita di Pavia, 27100 Pavia, Italy. 1J. P. Boucher, L. P. Regnault, J. Rossad Miguod, J. P. Renard, J. Bouillot, and W. G. Stirling, J. Appl. Phys. 52, 1956 (1981). 2K. M. Leung, D. Hone, D. L. Mills, P. S. Riseborough, and S. E. Trullinger, Phys. Rev. B 21, 4017 (1980).

  15. Comparison of AC losses, magnetic field/current distributions and critical currents of superconducting circular pancake coils and infinitely long stacks using coated conductors

    NASA Astrophysics Data System (ADS)

    Yuan, Weijia; Campbell, A. M.; Hong, Z.; Ainslie, M. D.; Coombs, T. A.

    2010-08-01

    A model is presented for calculating the AC losses, magnetic field/current density distribution and critical currents of a circular superconducting pancake coil. The assumption is that the magnetic flux lines will lie parallel to the wide faces of tapes in the unpenetrated area of the coil. Instead of using an infinitely long stack to approximate the circular coil, this paper gives an exact circular coil model using elliptic integrals. A new efficient numerical method is introduced to yield more accurate and fast computation. The computation results are in good agreement with the assumptions. For a small value of the coil radius, there is an asymmetry along the coil radius direction. As the coil radius increases, this asymmetry will gradually decrease, and the AC losses and penetration depth will increase, but the critical current will decrease. We find that if the internal radius is equal to the winding thickness, the infinitely long stack approximation overestimates the loss by 10% and even if the internal radius is reduced to zero, the error is still only 60%. The infinitely long stack approximation is therefore adequate for most practical purposes. In addition, the comparison result shows that the infinitely long stack approximation saves computation time significantly.

  16. Ac magnetotransport in La 0.7Sr 0.3Mn 0.95Fe 0.05O 3 at low dc magnetic fields

    NASA Astrophysics Data System (ADS)

    Barik, S. K.; Mahendiran, R.

    2011-12-01

    We report the ac electrical response of La 0.7Sr 0.3Mn 1- xFe xO 3(x=0.05) as a function of temperature, magnetic field (H) and frequency of radio frequency ( rf) current ( f=0.1-20 MHz). The ac impedance (Z) was measured while rf current directly passes through the sample as well as in a coil surrounding the sample. It is found that with increasing frequency of the rf current, Z(T) shows an abrupt increase accompanied by a peak at the ferromagnetic Curie temperature. The peak decreases in magnitude and shifts down with increasing value of H. We find a magnetoimpedance of ΔZ/Z=-21% for ΔH=500 Oe at f=1 MHz around room temperature when the rf current flows directly through the sample and ΔZ/Z=-65.9% when the rf current flows through a coil surrounding the sample. It is suggested that the magnetoimpedance observed is a consequence of suppression of transverse permeability which enhances skin depth for current flow. Our results indicate that the magnetic field control of high frequency impedance of manganites is more useful than direct current magnetoresistance for low-field applications.

  17. Fast-ion losses induced by ELMs and externally applied magnetic perturbations in the ASDEX Upgrade tokamak

    NASA Astrophysics Data System (ADS)

    Garcia-Munoz, M.; Äkäslompolo, S.; de Marne, P.; Dunne, M. G.; Dux, R.; Evans, T. E.; Ferraro, N. M.; Fietz, S.; Fuchs, C.; Geiger, B.; Herrmann, A.; Hoelzl, M.; Kurzan, B.; Lazanyi, N.; McDermott, R. M.; Nocente, M.; Pace, D. C.; Rodriguez-Ramos, M.; Shinohara, K.; Strumberger, E.; Suttrop, W.; Van Zeeland, M. A.; Viezzer, E.; Willensdorfer, M.; Wolfrum, E.

    2013-12-01

    Phase-space time-resolved measurements of fast-ion losses induced by edge localized modes (ELMs) and ELM mitigation coils have been obtained in the ASDEX Upgrade tokamak by means of multiple fast-ion loss detectors (FILDs). Filament-like bursts of fast-ion losses are measured during ELMs by several FILDs at different toroidal and poloidal positions. Externally applied magnetic perturbations (MPs) have little effect on plasma profiles, including fast-ions, in high collisionality plasmas with mitigated ELMs. A strong impact on plasma density, rotation and fast-ions is observed, however, in low density/collisionality and q95 plasmas with externally applied MPs. During the mitigation/suppression of type-I ELMs by externally applied MPs, the large fast-ion bursts observed during ELMs are replaced by a steady loss of fast-ions with a broad-band frequency and an amplitude of up to an order of magnitude higher than the neutral beam injection (NBI) prompt loss signal without MPs. Multiple FILD measurements at different positions, indicate that the fast-ion losses due to static 3D fields are localized on certain parts of the first wall rather than being toroidally/poloidally homogeneously distributed. Measured fast-ion losses show a broad energy and pitch-angle range and are typically on banana orbits that explore the entire pedestal/scrape-off-layer (SOL). Infra-red measurements are used to estimate the heat load associated with the MP-induced fast-ion losses. The heat load on the FILD detector head and surrounding wall can be up to six times higher with MPs than without 3D fields. When 3D fields are applied and density pump-out is observed, an enhancement of the fast-ion content in the plasma is typically measured by fast-ion D-alpha (FIDA) spectroscopy. The lower density during the MP phase also leads to a deeper beam deposition with an inward radial displacement of ≈2 cm in the maximum of the beam emission. Orbit simulations are used to test different models for 3D

  18. p -shell carrier assisted dynamic nuclear spin polarization in single quantum dots at zero external magnetic field

    NASA Astrophysics Data System (ADS)

    Fong, C. F.; Ota, Y.; Harbord, E.; Iwamoto, S.; Arakawa, Y.

    2016-03-01

    Repeated injection of spin-polarized carriers in a quantum dot (QD) leads to the polarization of nuclear spins, a process known as dynamic nuclear spin polarization (DNP). Here, we report the observation of p-shell carrier assisted DNP in single QDs at zero external magnetic field. The nuclear field—measured by using the Overhauser shift of the singly charged exciton state of the QDs—continues to increase, even after the carrier population in the s-shell saturates. This is also accompanied by an abrupt increase in nuclear spin buildup time as p-shell emission overtakes that of the s shell. We attribute the observation to p-shell electrons strongly altering the nuclear spin dynamics in the QD, supported by numerical simulation results based on a rate equation model of coupling between electron and nuclear spin system. Dynamic nuclear spin polarization with p-shell carriers could open up avenues for further control to increase the degree of nuclear spin polarization in QDs.

  19. Electron acceleration based on a laser pulse propagating through a plasma in the simultaneous presence of a helical wiggler and an obliquely applied external magnetic field

    NASA Astrophysics Data System (ADS)

    Gashti, M. A.; Jafari, S.

    2016-06-01

    Electron acceleration based on a laser pulse propagating through plasma channel has been studied in the simultaneous presence of a helical magnetic wiggler and an obliquely applied external magnetic field. A numerical study of electron energy and electron trajectory has been made using the fourth-order Runge-kutta method. Numerical results indicate that electron energy increases with decreasing θ -angle of the obliquely external magnetic field. Besides, it increases with increasing the amplitude of the obliquely magnetic field. It is also found that the electron attains a higher energy at shorter distances for higher amplitude of the wiggler field Ωw . Therefore, employing a magnetic wiggler field is very beneficial for electron acceleration in short distances. Further new results reveal that in the absence of the wiggler field (Ωw=0) , the electron energy increases with increasing the laser intensity, whereas in the presence of the wiggler field (Ωwneq0) , the electron energy increases with decreasing the laser intensity. As a result, employing a wiggler magnetic field in the laser-based electron accelerators can be worthwhile in the design of table top accelerators and it can enhance the electron energy at lower laser intensities.

  20. External split field generator

    SciTech Connect

    Thundat, Thomas George; Van Neste, Charles W.; Vass, Arpad Alexander

    2012-02-21

    A generator includes a coil disposed about a core. A first stationary magnetic field source may be disposed on a first end portion of the core and a second stationary magnetic field source may be disposed on a second end portion of core. The first and second stationary magnetic field sources apply a stationary magnetic field to the coil. An external magnetic field source may be disposed outside the coil to apply a moving magnetic field to the coil. Electrical energy is generated in response to an interaction between the coil, the moving magnetic field, and the stationary magnetic field.

  1. Detail study on ac-dc magnetic and dye absorption properties of Fe3O4 hollow spheres for biological and industrial application.

    PubMed

    Sarkar, Debasish; Mandal, Kalyan; Mandal, Madhuri

    2014-03-01

    Here solvo-thermal technique has been used to synthesize hollow-nanospheres of magnetite. We have shown that PVP plays an important role to control the particle size and also helps the particles to take the shape of hollow spheres. Structural analysis was done by XRD measurement and morphological measurements like SEM and TEM were performed to confirm the hollow type spherical particles formation and their shape and sizes were also investigated. The detail ac-dc magnetic measurements give an idea about the application of these nano spheres for hyperthermia therapy and spontaneous dye adsorption properties (Gibbs free energy deltaG0 = -0.526 kJ/mol for Eosin and -1.832 kJ/mol for MB) of these particles indicate its use in dye manufacturing company. Being hollow in structure and magnetic in nature such materials will also be useful in other application fields like in drug delivery, arsenic and heavy metal removal by adsorption technique, magnetic separation etc. PMID:24745226

  2. Dynamic Contrast-Enhanced Magnetic Resonance Imaging for Localization of Recurrent Prostate Cancer After External Beam Radiotherapy

    SciTech Connect

    Haider, Masoom A. Chung, Peter; Sweet, Joan; Toi, Ants; Jhaveri, Kartik; Menard, Cynthia; Warde, Padraig; Trachtenberg, John; Lockwood, Gina M.Math.; Milosevic, Michael

    2008-02-01

    Purpose: To compare the performance of T2-weighted (T2w) imaging and dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) of the prostate gland in the localization of recurrent prostate cancer in patients with biochemical failure after external beam radiotherapy (EBRT). Methods and Materials: T2-weighted imaging and DCE MRI were performed in 33 patients with suspected relapse after EBRT. Dynamic contrast-enhanced MRI was performed with a temporal resolution of 95 s. Voxels enhancing at 46 s after injection to a greater degree than the mean signal intensity of the prostate at 618 s were considered malignant. Results from MRI were correlated with biopsies from six regions in the peripheral zone (PZ) (base, mid, and apex). The percentage of biopsy core positive for malignancy from each region was correlated with the maximum diameter of the tumor on DCE MRI with a linear regression model. Results: On a sextant basis, DCE MRI had significantly better sensitivity (72% [21of 29] vs. 38% [11 of 29]), positive predictive value (46% [21 of 46] vs. 24% [11 of 45]) and negative predictive value (95% [144 of 152] vs. 88% [135 of 153] than T2w imaging. Specificities were high for both DCE MRI and T2w imaging (85% [144 of 169] vs. 80% [135 of 169]). There was a linear relationship between tumor diameters on DCE MRI and the percentage of cancer tissue in the corresponding biopsy core (r = 0.9, p < 0.001), with a slope of 1.2. Conclusions: Dynamic contrast-enhanced MRI performs better than T2w imaging in the detection and localization of prostate cancer in the peripheral zone after EBRT. This may be helpful in the planning of salvage therapy.

  3. Experimental observation of further frequency upshift from dc to ac radiation converter with perpendicular dc magnetic field

    PubMed

    Higashiguchi; Yugami; Gao; Niiyama; Sasaki; Takahashi; Ito; Nishida

    2000-11-20

    A frequency upshift of a short microwave pulse is generated by the interaction between a relativistic underdense ionization front and a periodic electrostatic field with a perpendicular dc magnetic field. When the dc magnetic field is applied, further frequency upshift of 3 GHz is observed with respect to an unmagnetized case which has typically a GHz range. The radiation frequency depends on both the plasma density and the strength of the dc magnetic field, i.e., the plasma frequency and the cyclotron frequency. The frequency of the emitted radiation is in reasonable agreement with the theoretical values. PMID:11082591

  4. Efficiency of the SQUID ratchet driven by external current

    NASA Astrophysics Data System (ADS)

    Spiechowicz, J.; Łuczka, J.

    2015-02-01

    We study theoretically the efficiency of an asymmetric superconducting quantum interference device (SQUID) which is constructed as a loop with three capacitively and resistively shunted Josephson junctions. Two junctions are placed in series in one arm and the remaining one is located in the other arm. The SQUID is threaded by an external magnetic flux and driven by an external current of both constant (dc) and time periodic (ac) components. This system acts as a nonequilibrium ratchet for the dc voltage across the SQUID with the external current as a source of energy. We analyze the power delivered by the external current and find that it strongly depends on thermal noise and the external magnetic flux. We explore a space of the system parameters to reveal a set for which the SQUID efficiency is globally maximal. We detect the intriguing feature of the thermal noise enhanced efficiency and show how the efficiency of the device can be tuned by tailoring the external magnetic flux.

  5. Nonlinear dynamics and chaotization of oscillations of a virtual cathode in an annular electron beam in a uniform external magnetic field

    NASA Astrophysics Data System (ADS)

    Kurkin, S. A.; Koronovski, A. A.; Hramov, A. E.

    2009-08-01

    Results are presented from a numerical study of the effect of an external magnetic field on the conditions and mechanisms for the formation of a virtual cathode in a relativistic electron beam. Characteristic features of the nonlinear dynamics of an electron beam with a virtual cathode are considered when the external magnetic field is varied. Various mechanisms are investigated by which the virtual cathode oscillations become chaotic and their spectrum becomes a multifrequency spectrum, thereby complicating the dynamics of the vircator system. A general mechanism for chaotization of the oscillations of a virtual cathode in a vircator system is revealed: the electron structures that form in an electron beam interact by means of a common space charge field to give rise to additional internal feedback. That the oscillations of a virtual cathode change from the chaotic to the periodic regime is due to the suppression of the mechanism for forming secondary electron structures.

  6. Hiding objects in AC magnetic fields of power grid frequency by two-shell ferromagnetic/superconducting cloak

    NASA Astrophysics Data System (ADS)

    Šouc, J.; Solovyov, M.; Gömöry, F.

    2016-07-01

    Performance of magnetic cloak made from commercially available materials has been tested by verifying its ability to suppress the magnetic signatures of metallic and ferromagnetic objects. The range of magnetic field amplitudes from 0.1 to 10 mT and frequencies around 50-60 Hz were used. The cloak combines the inner tube from high-temperature superconductor that should be cooled by liquid nitrogen, with the outer tube made from MnZn ferrite powder mixed in plastic matter. Superconductor is in the form of tapes wound in helical manner on a round former. Such design is promising when the objects with dimensions reaching several centimeters should be cloaked. Performance of the small model manufactured following this design was demonstrated by observing ˜20 times reduction of the magnetic signature of metallic or ferromagnetic objects.

  7. Specific absorption rate dependence on temperature in magnetic field hyperthermia measured by dynamic hysteresis losses (ac magnetometry)

    NASA Astrophysics Data System (ADS)

    Garaio, Eneko; Sandre, Olivier; Collantes, Juan-Mari; Garcia, Jose Angel; Mornet, Stéphane; Plazaola, Fernando

    2015-01-01

    Magnetic nanoparticles (NPs) are intensively studied for their potential use for magnetic hyperthermia, a treatment that has passed a phase II clinical trial against severe brain cancer (glioblastoma) at the end of 2011. Their heating power, characterized by the ‘specific absorption rate (SAR)’, is often considered temperature independent in the literature, mainly because of the difficulties that arise from the measurement methodology. Using a dynamic magnetometer presented in a recent paper, we measure here the thermal dependence of SAR for superparamagnetic iron oxide (maghemite) NPs of four different size-ranges corresponding to mean diameters around 12 nm, 14 nm, 15 nm and 16 nm. The article reports a parametrical study extending from 10 to 60 {}^\\circ C in temperature, from 75 to 1031 kHz in frequency, and from 2 to 24 kA m-1 in magnetic field strength. It was observed that SAR values of smaller NPs decrease with temperature whereas for the larger sample (16 nm) SAR values increase with temperature. The measured variation of SAR with temperature is frequency dependent. This behaviour is fully explained within the scope of linear response theory based on Néel and Brown relaxation processes, using independent magnetic measurements of the specific magnetization and the magnetic anisotropy constant. A good quantitative agreement between experimental values and theoretical values is confirmed in a tri-dimensional space that uses as coordinates the field strength, the frequency and the temperature.

  8. Probing Interfacial Friction and Dissipation in Granular Gold­ Nickel Alloys with a Quartz Crystal Oscillator in an External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Stevens, K. M.; Krim, J.

    2015-03-01

    We present here a quartz crystal microbalance study of two-phase gold nickel alloys whose internal granular properties are probed by exposure to a fluctuating external magnetic field. The work is motivated by prior studies demonstrating that granular two-phase materials exhibited lower friction and wear than solid solution alloys with identical compositions. In particular, we report a ``flexing'' effect which appears when an external magnetic field is applied, and is manifested as a decrease in the magnitude of oscillation amplitude that is synchronized with the applied field; the effect is not seen on the complimentary solid solution samples. The effect is consistent with internal interfacial friction between nickel and gold grains, indicating a degree of freedom which may decrease friction even in the absence of an external magnetic field. This is supported through analysis of energy dissipation in the system, using the Butterworth­-Van Dyke equivalent circuit model. Data and interpretation are also presented that rule out alternate explanations such as giant magnetoresistance and/or other resistive phenomenon within the film. Funding provided by NSF DMR0805204. Thanks to L. Pan for sample preparation.

  9. Numerical investigations on a compact magnetic fusion device for studying the effect of external applied magnetic field oscillations on the nuclear burning efficiency of D-T and p-11B fuels

    NASA Astrophysics Data System (ADS)

    Moustaizis, S. D.; Lalousis, P.; Hora, H.; Larour, J.; Auvray, P.; Balcou, P.; Ducret, J.-E.; Martin, P.

    2015-05-01

    The burning process of high density (about 1018cm-3), high temperature (tens to hundreds of keV) plasma trapped by a high mirror-like magnetic field in a Compact Magnetic Fusion (CMF) device is numerically investigated.. The initial high density and high temperature plasma in the CMF device is produced by ultrashort high intensity laser beam interaction with clusters or thin foils, and two fuels, D-T and p-11B are studied. The spatio-temporal evolution of D-T and p-11B plasmas, the production of alphas, the generated electric fields and the high external applied magnetic field are described by a 1-D multifluid code. The initial values for the plasma densities, temperatures and external applied magnetic field (about 100 T) correspond to high β plasmas. The main objectives of the numerical simulations are: to study the plasma trapping, the neutron and alpha production for both fuels, and compare the effect of the external applied magnetic field on the nuclear burning efficiency for the two fuels.. The comparisons and the advantages for each fuel will be presented. The proposed CMF device and the potential operation of the device within the ELI-NP pillar will be discussed.

  10. AC Circuit Measurements with a Differential Hall Element Magnetometer

    NASA Astrophysics Data System (ADS)

    Calkins, Matthew W.; Nicks, B. Scott; Quintero, Pedro A.; Meisel, Mark W.

    2013-03-01

    As the biomedical field grows, there is an increasing need to quickly and efficiently characterize more samples at room temperature. An automated magnetometer was commissioned to do these room temperature magnetic characterizations. This magnetometer, which is inspired by a Differential Hall Element Magnetometer,[2] uses two commercially available Hall elements wired in series. One Hall element measures the external magnetic field of a 9 T superconducting magnet and the other measures the same external field plus the field due to the magnetization of the sample that sits on top of the Hall element. The difference between these two Hall elements is taken while a linear stepper motor sweeps through the external magnetic field. The linear motor and data acquisition are controlled by a LabVIEW program. Recently, the system was outfitted for AC circuit measurements and these data will be compared to DC circuit data. In addition, the lowest signal to noise ratio will be found in order to deduce the smallest amount of sample needed to register an accurate coercive field. Supported by the NSF via NHMFL REU (DMR-0654118), a single investigator grant (DMR-1202033 to MWM) and by the UF Undergraduate Scholars Program.

  11. Experimental Study on Current Decay Characteristics of Persistent Current HTS Magnet by Alternating Magnetic Field

    NASA Astrophysics Data System (ADS)

    Park, Young Gun; Lee, Chang Young; Hwang, Young Jin; Lee, Woo Seung; Lee, Jiho; Jo, Hyun Chul; Chung, Yoon Do; Ko, Tae Kuk

    This paper deals with a current decay characteristics of a high temperature superconducting (HTS) magnet operated in persistent current mode (PCM). In superconducting synchronous machine applications such as linear synchronous motor (LSM), the superconducting coil is designed to operate in the PCM to obtain steady magnetic field with DC transport current. This superconducting magnet operates on a direct current, but it can be exposed to alternating magnetic field due to the armature winding. When the magnet is subjected to an external time-varying magnetic field, it is possible to result in a decay of the current in PCM system due to AC loss. In this research, a PCM system with armature coil which generates time-varying magnetic field was fabricated to verify current decay characteristics by external alternating magnetic field. The current decay rate was measured by using a hall sensor as functions of amplitude and frequency of armature coil.

  12. Slow Relaxation of Magnetization in an Isostructural Series of Zinc-Lanthanide Complexes: An Integrated EPR and AC Susceptibility Study.

    PubMed

    Amjad, Asma; Madalan, Augustin M; Andruh, Marius; Caneschi, Andrea; Sorace, Lorenzo

    2016-08-26

    We report the synthesis, structure, and spectroscopic and dynamic magnetic properties of a series of heterodinuclear complexes, [ZnLn(LH4 )2 ](NO3 )3 ⋅6 H2 O (Ln=Nd, Tb, Dy, Ho, Er, and Yb), with the singly deprotonated form of a new compartmentalized Schiff-base ligand, LH5 . The Ln(III) ions in these systems show a distorted square-antiprism geometry with an LnO8 coordination sphere. EPR spectroscopy and DC magnetic studies have shown that the anisotropic nature of the complexes is far more complicated than predicted on the basis of a simple electrostatic model. Among the investigated systems, only the Dy(III) derivative showed single-ion magnet behavior, in zero and an applied magnetic field, both in pure polycrystalline samples and in a series of polycrystalline samples with different degrees of dilution at the single-crystal level in the isostructural Y(III) derivative. The rich dynamics observed as functions of frequency, field, and temperature reveals that multiple relaxation mechanisms are at play, resulting in a barrier of 189 cm(-1) , which is among the highest reported for a dinuclear Zn-Dy system. Analysis of the dynamic behavior as a function of dilution degree further evidenced the persistence of non-negligible intermolecular interactions, even at the lowest concentration of 1 %. PMID:27465998

  13. ELECTRICAL AND ELECTRONIC INDUSTRIAL CONTROL. A-C CONVENTIONAL MAGNETIC MOTOR CONTROL, PART I, UNIT 5, ASSIGNMENTS.

    ERIC Educational Resources Information Center

    SUTTON, MACK C.

    THIS GUIDE IS FOR INDIVIDUAL STUDENT USE IN STUDYING ALTERNATING CURRENT CONVENTIONAL MAGNETIC MOTOR CONTROL IN ELECTRICAL-ELECTRONIC PROGRAMS. IT WAS DEVELOPED BY AN INSTRUCTIONAL MATERIALS SPECIALIST AND ADVISERS. EACH OF THE 10 ASSIGNMENT SHEETS PROVIDES THE LESSON SUBJECT, PURPOSE, INTRODUCTORY INFORMATION, STUDY REFERENCES, SUPPLEMENTARY…

  14. ELECTRICAL AND ELECTRONIC INDUSTRIAL CONTROL. A-C CONVENTIONAL MAGNETIC MOTOR CONTROL, PART I, UNIT 5, INSTRUCTOR'S GUIDE.

    ERIC Educational Resources Information Center

    SUTTON, MACK C.

    THIS GUIDE IS FOR TEACHER USE IN DIRECTING INDIVIDUAL STUDY OF ALTERNATING CURRENT CONVENTIONAL MAGNETIC MOTOR CONTROL IN ELECTRICAL-ELECTRONIC PROGRAMS. IT WAS DEVELOPED BY AN INSTRUCTIONAL MATERIALS SPECIALIST AND ADVISERS. EACH OF THE 10 INSTRUCTOR'S SHEETS GIVES THE LESSON SUBJECT, PURPOSE, INTRODUCTORY INFORMATION, REFERENCES, AND…

  15. ELECTRICAL AND ELECTRONIC INDUSTRIAL CONTROL. A-C CONVENTIONAL MAGNETIC MOTOR CONTROL, PART II, UNIT 6, INSTRUCTOR'S GUIDE.

    ERIC Educational Resources Information Center

    SUTTON, MACK C.

    THIS GUIDE IS FOR TEACHER USE IN DIRECTING INDIVIDUAL STUDY OF ALTERNATING CURRENT CONVENTIONAL MAGNETIC MOTOR CONTROL IN ELECTRICAL-ELECTRONIC PROGRAMS. IT WAS DEVELOPED BY AN INSTRUCTIONAL MATERIALS SPECIALIST AND ADVISERS. EACH OF THE 10 INSTRUCTOR'S SHEETS GIVES THE LESSON SUBJECT, PURPOSE, INTRODUCTORY INFORMATION, REFERENCES, SUPPLEMENTARY…

  16. ELECTRICAL AND ELECTRONIC INDUSTRIAL CONTROL. A-C CONVENTIONAL MAGNETIC MOTOR CONTROL, PART II, UNIT 6, ASSIGNMENTS.

    ERIC Educational Resources Information Center

    SUTTON, MACK C.

    THIS STUDY GUIDE IS FOR INDIVIDUAL STUDENT USE IN STUDYING ALTERNATING CURRENT CONVENTIONAL MAGNETIC MOTOR CONTROL IN ELECTRICAL-ELECTRONIC PROGRAMS. IT WAS DEVELOPED BY AN INSTRUCTIONAL MATERIALS SPECIALIST AND ADVISERS. EACH OF THE 10 ASSIGNMENT SHEETS PROVIDES THE LESSON SUBJECT, PURPOSE, INTRODUCTORY INFORMATION, STUDY REFERENCES,…

  17. Controlling the Goos-Hänchen shift with external electric and magnetic fields in an electro-optic/magneto-electric heterostructure

    NASA Astrophysics Data System (ADS)

    Dadoenkova, Yu. S.; Bentivegna, F. F. L.; Dadoenkova, N. N.; Petrov, R. V.; Lyubchanskii, I. L.; Bichurin, M. I.

    2016-05-01

    We present a theoretical investigation of the Goos-Hänchen effect upon light reflection from a heterostructure consisting of an electro-optic film deposited on a magneto-electric film grown on a nonmagnetic dielectric substrate. It is shown that the linear magneto-electric interaction leads to an increase of the lateral shift even in the absence of any applied electric field. The presence of the electro-optic layer enables the control of the Goos-Hänchen shift and of the position of its maximum (with respect to the angle of incidence) through a variation of the magnitude and orientation of an applied electric field. It is also demonstrated that applying an external magnetic field in order to reverse the magnetization in the magnetic layer results (under the influence of the magneto-electric interaction in the system) in a sign reversal of the lateral shift but a nonreciprocal change of its amplitude.

  18. Magnetic structure of U2Rh3Si5 in external fields up to 14.5 T

    NASA Astrophysics Data System (ADS)

    Galli, F.; Feyerherm, R.; Prokes, K.; Nieuwenhuys, G. J.

    2000-03-01

    The intermetallic compound U2Rh3Si5 exhibits a first-order transition at 25 K into a noncollinear antiferromagnetic structure. At the lowest temperature the antiferromagnetic structure can be destroyed by a field of 14 T. Using the two-axis spectrometer E4 at the Hahn-Meitner-Institute, we have studied the magnetic structure of U2Rh3Si5 for various temperatures and magnetic fields around the magnetic phase boundary.

  19. Effect of external magnetic field on the co-existence of superconductivity and antiferromagnetism in rare earth nickel borocarbides (RNi2B2C)

    NASA Astrophysics Data System (ADS)

    Das, Salila; Padhi, Prakash Chandra

    2016-03-01

    In this paper, we have studied the effect of external magnetic field in the co-existing phase of superconducting and antiferromagnetism (AFM) of rare earth nickel borocarbides. The AFM in these systems might have originated due to both localized “f” electrons as well as itinerant electrons which are responsible for conduction. On the other hand, superconductivity (SC) is due to spin density wave, arising out of Fermi surface instability. The AFM order is mostly influenced by hybridization of the “f” electron with the conduction electron. Here, we have obtained the dependence of superconducting energy gap as well as staggered magnetic field on temperature T and energy ɛk in a framework based on mean field Hamiltonian using double time electron Green’s function. We have shown in our calculation the effect of external magnetic field on superconducting and antiferromagnetic order parameters for YNi2B2C in the presence of hybridization. The ratio of the calculated effective gap and TC is close to BCS value which agrees quite well with experimental results.

  20. Donor impurity states and related terahertz range nonlinear optical response in GaN cylindrical quantum wires: Effects of external electric and magnetic fields

    SciTech Connect

    Correa, J. D.; Mora-Ramos, M. E.; Duque, C. A.

    2014-06-07

    We report a study on the optical absorption coefficient associated to hydrogenic impurity interstate transitions in zinc-blende GaN quantum wires of cylindrical shape taking into account the effects of externally applied static electric and magnetic fields. The electron states emerge within the effective mass approximation, via the exact diagonalization of the donor-impurity Hamiltonian with parabolic confinement and external field effects. The nonlinear optical absorption is calculated using a recently derived expression for the dielectric susceptibility, obtained via a nonperturbative solution of the density-matrix Bloch equation. Our results show that this treatment eliminates not only the intensity-dependent bleaching effect but also the change in sign of the nonlinear contribution due to the combined effect of asymmetric impurity location and the applied electric field.

  1. Donor impurity states and related terahertz range nonlinear optical response in GaN cylindrical quantum wires: Effects of external electric and magnetic fields

    NASA Astrophysics Data System (ADS)

    Correa, J. D.; Mora-Ramos, M. E.; Duque, C. A.

    2014-06-01

    We report a study on the optical absorption coefficient associated to hydrogenic impurity interstate transitions in zinc-blende GaN quantum wires of cylindrical shape taking into account the effects of externally applied static electric and magnetic fields. The electron states emerge within the effective mass approximation, via the exact diagonalization of the donor-impurity Hamiltonian with parabolic confinement and external field effects. The nonlinear optical absorption is calculated using a recently derived expression for the dielectric susceptibility, obtained via a nonperturbative solution of the density-matrix Bloch equation. Our results show that this treatment eliminates not only the intensity-dependent bleaching effect but also the change in sign of the nonlinear contribution due to the combined effect of asymmetric impurity location and the applied electric field.

  2. Finite element modeling study of the suppression effect of external high magnetic field on the heat transfer of tungsten melt

    NASA Astrophysics Data System (ADS)

    Qu, S.; Jia, Y.; Gao, S.; Yuan, Y.; Li, C.; Lian, Y.; Liu, X.; Liu, W.

    2016-02-01

    Finite element modeling analysis has been employed to simulate the melt layer motion of tungsten and tungsten-based materials under high magnetic field. High heat flux of 2 GW m-2 was loaded for 3 ms at 1000 K and provided a molten bath. Meanwhile, high magnetic field from 0 to 8 T was loaded during the simulation. Both positive and negative surface tension temperature coefficient was tested. The result shows that the convention forced by the surface tension is suppressed by the magnetic field. The high magnetic field performs as a resistance of the heat transfer, leading to a reduced molten bath. The magnetic field mitigates the melting behaviur of the tungsten materials.

  3. Modified Solenoid Coil That Efficiently Produces High Amplitude AC Magnetic Fields With Enhanced Uniformity for Biomedical Applications

    PubMed Central

    Bordelon, David E.; Goldstein, Robert C.; Nemkov, Valentin S.; Kumar, Ananda; Jackowski, John K.; DeWeese, Theodore L.; Ivkov, Robert

    2014-01-01

    In this paper, we describe a modified solenoid coil that efficiently generates high amplitude alternating magnetic fields (AMF) having field uniformity (≤10%) within a 125-cm3 volume of interest. Two-dimensional finite element analysis (2D-FEA) was used to design a coil generating a targeted peak AMF amplitude along the coil axis of ~100 kA/m (peak-to-peak) at a frequency of 150 kHz while maintaining field uniformity to >90% of peak for a specified volume. This field uniformity was realized by forming the turns from cylindrical sections of copper plate and by adding flux concentrating rings to both ends of the coil. Following construction, the field profile along the axes of the coil was measured. An axial peak field value of 95.8 ± 0.4 kA/m was measured with 650 V applied to the coil and was consistent with the calculated results. The region of axial field uniformity, defined as the distance over which field ≥90% of peak, was also consistent with the simulated results. We describe the utility of such a device for calorimetric measurement of nanoparticle heating for cancer therapy and for magnetic fluid hyperthermia in small animal models of human cancer. PMID:25392562

  4. Determination of Arterial Blood Flow by Percutaneously Introduced Flow Sensors in an External Magnetic Field, II. Implementation of the Method In Vivo*

    PubMed Central

    Kolin, Alexander; Grollman, Julius H.; Steckel, Richard J.; Snow, Harold D.

    1971-01-01

    Blood flow in a dog's aorta has been measured by percutaneous introduction of a flow sensor. Two types of flow probes have been used in conjunction with an external magnetic field: Loop-shaped probes used as rate of volume-flow meters and L-shaped probes as velometers. Methods of calibration and establishing the base line are discussed, and the performance of the apparatus is illustrated by records of blood flow in the thoracic and abdominal regions of the aorta. Images PMID:5276298

  5. Generalization of the Bennett equilibrium condition for a relativistic electron beam propagating in the Ohmic plasma channel and ion focusing regime along an external magnetic field

    NASA Astrophysics Data System (ADS)

    Kolesnikov, E. K.; Manuilov, A. S.

    2016-04-01

    The problem of formulating the generalization of the Bennett equilibrium condition is considered for a relativistic electron beam propagating in the Ohmic plasma channel, as well as in the ion focusing regime in the presence of an external longitudinal uniform magnetic field. We assume that the electron component of the background plasma is not completely removed from the region occupied by the beam. This equilibrium condition is derived using the mass and momentum transport equations obtained for a paraxial monoenergetic beam from the Fokker-Planck kinetic equation.

  6. Strong dependence of spin dynamics on the orientation of an external magnetic field for InSb and InAs

    NASA Astrophysics Data System (ADS)

    Litvinenko, K. L.; Leontiadou, M. A.; Li, Juerong; Clowes, S. K.; Emeny, M. T.; Ashley, T.; Pidgeon, C. R.; Cohen, L. F.; Murdin, B. N.

    2010-03-01

    Electron spin relaxation times have been measured in InSb and InAs epilayers in a moderate (<4 T) external magnetic field. A strong and opposite field dependence of the spin lifetime was observed for longitudinal (Faraday) and transverse (Voigt) configuration. In the Faraday configuration the spin lifetime increases because the D'yakonov-Perel' dephasing process is suppressed. At the high field limit the Elliot-Yafet spin flip relaxation process dominates, enabling its direct determination. Conversely, as predicted theoretically for narrow band gap semiconductors, an additional efficient spin dephasing mechanism dominates in the Voigt configuration significantly decreasing the electron spin lifetime with increasing field.

  7. Tuning friction with an external magnetic field: A Quartz Crystal Microbalance study of physisorbed oxygen monolayers and multilayers sliding on nickel substrates

    NASA Astrophysics Data System (ADS)

    Fredricks, Z. B.; Stevens, K. M.; Acharya, B.; Krim, J.

    The sliding friction levels of oxygen monolayer and multilayer films adsorbed on nickel close to the oxygen monolayer solid-liquid melting transition temperature have been monitored by means of a Quartz Crystal Microbalance (QCM) technique in the presence and absence of a weak external magnetic field. Friction levels for the monolayers in the presence of the field were observed to be half of those observed in the absence of a field. For thick films, the reduction was proportionately less, indicating an interfacial effect as the source of the magnetic sensitivity. While the presence of the field is expected to increase the normal force between the paramagnetic oxygen overlayer and the ferromagnetic substrate, the impact of this mechanism on friction appears to be minimal, or possibly masked by more dominant mechanisms. These include magnetically induced structural reorientation (magnetostriction), and/or realignment of adlayer spins in response to the applied field, both of which would reduce the physical or magnetic interfacial commensurability, thus lowering friction levels. Work supported by NSF DMR1310456.

  8. The Effect of an External Magnetic Field on the Plume Expansion Dynamics of Laser-Induced Aluminum Plasma

    NASA Astrophysics Data System (ADS)

    Atif, Hussain; Li, Qi; Hao, Zuoqiang; Gao, Xun; Lin, Jingquan

    2015-08-01

    In this work, we investigated the plasma morphology induced by a Nd:YAG laser with the aim of improving the understanding of the formation and dynamics of the plasma in two cases, with and without a magnetic field. Single laser pulse production of a plasma in the absence and presence of a magnetic field was performed with an aluminum target in air. A fast photography technique was employed to obtain information about the expansion dynamics and confinement of the aluminum plasma in each case. The generation of the laser plasma was allowed to expand at two locations with different magnetic field strengths, which correspond to the strength 0.58 T in the center of two magnetic poles and 0.83 T at a distance of 4 mm from the upper pole (N). The plume showed lateral confinement at longer delays when the target was placed at the center of the two poles. When the target was placed at a distance of 4 mm from the upper pole it was observed that the plume was divided into two lobes at the initial stage and traveled towards the center of the magnetic field with further elapse of time. supported by National Natural Science Foundation of China (No. 61178022), the Research Foundation for Doctoral Program of Higher Education of China (Nos. 20112216120006, 20122216120009 and 20122216110007) and also the Project of 14KP007

  9. Quasi-discrete particle motion in an externally imposed, ordered structure in a dusty plasma at high magnetic field

    NASA Astrophysics Data System (ADS)

    Thomas, Edward; Konopka, Uwe; Lynch, Brian; Adams, Stephen; LeBlanc, Spencer; Merlino, Robert L.; Rosenberg, Marlene

    2015-11-01

    Dusty plasmas have been studied in argon, radio frequency (rf) glow discharge plasmas at magnetic fields up to 2.5 T where the electrons and ions are strongly magnetized. Plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper electrode supports a dual mesh consisting of #24 brass and #30 aluminum wire cloth. In this experiment, we study the formation of imposed ordered structures and particle dynamics as a function of magnetic field. Through observations of trapped particles and the quasi-discrete (i.e., "hopping") motion of particles between the trapping locations, it is possible to make a preliminary estimate of the potential structure that confines the particles to a grid structure in the plasma. This information is used to gain insight into the formation of the imposed grid pattern of the dust particles in the plasma.

  10. Quasi-discrete particle motion in an externally imposed, ordered structure in a dusty plasma at high magnetic field

    SciTech Connect

    Thomas, Edward Konopka, Uwe; Lynch, Brian; Adams, Stephen; LeBlanc, Spencer; Merlino, Robert L.; Rosenberg, Marlene

    2015-11-15

    Dusty plasmas have been studied in argon, radio frequency (rf) glow discharge plasmas at magnetic fields up to 2.5 T where the electrons and ions are strongly magnetized. Plasmas are generated between two parallel plate electrodes where the lower, powered electrode is solid and the upper electrode supports a dual mesh consisting of #24 brass and #30 aluminum wire cloth. In this experiment, we study the formation of imposed ordered structures and particle dynamics as a function of magnetic field. Through observations of trapped particles and the quasi-discrete (i.e., “hopping”) motion of particles between the trapping locations, it is possible to make a preliminary estimate of the potential structure that confines the particles to a grid structure in the plasma. This information is used to gain insight into the formation of the imposed grid pattern of the dust particles in the plasma.

  11. Influence of the vector interaction and an external magnetic field on the isentropes near the chiral critical end point

    NASA Astrophysics Data System (ADS)

    Costa, Pedro

    2016-06-01

    The location of the critical end point (CEP) and the isentropic trajectories in the QCD phase diagram are investigated. We use the (2 +1 ) Nambu-Jona-Lasinio model with the Polyakov loop coupling for different scenarios, namely by imposing zero strange quark density, which is the case in the ultrarelativistic heavy ion collisions, and β equilibrium. The influence of strong magnetic fields and of the vector interaction on the isentropic trajectories around the CEP is discussed. It is shown that the vector interaction and the magnetic field, having opposite effects on the first-order transition, affect the isentropic trajectories differently: as the vector interaction increases, the first-order transition becomes weaker and the isentropes become smoother; when a strong magnetic field is considered, the first-order transition is strengthened and the isentropes are pushed to higher temperatures. No focusing of isentropes in region towards the CEP is seen.

  12. RHIC spin flipper AC dipole controller

    SciTech Connect

    Oddo, P.; Bai, M.; Dawson, C.; Gassner, D.; Harvey, M.; Hayes, T.; Mernick, K.; Minty, M.; Roser, T.; Severino, F.; Smith, K.

    2011-03-28

    The RHIC Spin Flipper's five high-Q AC dipoles which are driven by a swept frequency waveform require precise control of phase and amplitude during the sweep. This control is achieved using FPGA based feedback controllers. Multiple feedback loops are used to and dynamically tune the magnets. The current implementation and results will be presented. Work on a new spin flipper for RHIC (Relativistic Heavy Ion Collider) incorporating multiple dynamically tuned high-Q AC-dipoles has been developed for RHIC spin-physics experiments. A spin flipper is needed to cancel systematic errors by reversing the spin direction of the two colliding beams multiple times during a store. The spin flipper system consists of four DC-dipole magnets (spin rotators) and five AC-dipole magnets. Multiple AC-dipoles are needed to localize the driven coherent betatron oscillation inside the spin flipper. Operationally the AC-dipoles form two swept frequency bumps that minimize the effect of the AC-dipole dipoles outside of the spin flipper. Both AC bumps operate at the same frequency, but are phase shifted from each other. The AC-dipoles therefore require precise control over amplitude and phase making the implementation of the AC-dipole controller the central challenge.

  13. Charge state control in single InAs/GaAs quantum dots by external electric and magnetic fields

    SciTech Connect

    Tang, Jing; Cao, Shuo; Gao, Yunan; Sun, Yue; Jin, Kuijuan; Xu, Xiulai; Geng, Weidong; Williams, David A.

    2014-07-28

    We report a photoluminescence (PL) spectroscopy study of charge state control in single self-assembled InAs/GaAs quantum dots by applying electric and/or magnetic fields at 4.2 K. Neutral and charged exciton complexes were observed under applied bias voltages from −0.5 V to 0.5 V by controlling the carrier tunneling. The highly negatively charged exciton emission becomes stronger with increasing pumping power, arising from the fact that electrons have a smaller effective mass than holes and are more easily captured by the quantum dots. The integrated PL intensity of negatively charged excitons is affected significantly by a magnetic field applied along the sample growth axis. This observation is explained by a reduction in the electron drift velocity caused by an applied magnetic field, which increases the probability of non-resonantly excited electrons being trapped by localized potentials at the wetting layer interface, and results in fewer electrons distributed in the quantum dots. The hole drift velocity is also affected by the magnetic field, but it is much weaker.

  14. Modeling the response of a top hat electrostatic analyzer in an external magnetic field: Experimental validation with the Juno JADE-E sensor

    NASA Astrophysics Data System (ADS)

    Clark, G.; Allegrini, F.; McComas, D. J.; Louarn, P.

    2016-06-01

    We investigate the response function of an electrostatic analyzer when electron gyroradii in a magnetic field become comparable to the scale size of the sensor. This occurs when electrons have sufficiently small energies and are in a strong magnetic field. Through simulations and laboratory experiments with the Jovian Auroral Distribution Experiment-Electron (JADE-E) sensor, we observe the energy response, detection angle distribution, and geometric factor to change significantly. Using electro-optics simulation results, we develop semiempirical and empirical relationships that can be used for top hat electrostatic analyzers. We present a model based on these relationships that covers an energy range between 0.1 keV and 5 keV with a uniform external magnetic field magnitude between 0-3 G and verified that these relationships apply to JADE-E in a specially designed testing environment by comparing with the model. We find that the model agrees well with the JADE-E sensor validating it for top hat electrostatic analyzers more generally.

  15. Electronic and magnetic properties of armchair MoS{sub 2} nanoribbons under both external strain and electric field, studied by first principles calculations

    SciTech Connect

    Hu, Ting; Dong, Jinming; Zhou, Jian; Kawazoe, Yoshiyuki

    2014-08-14

    The electronic and magnetic properties of armchair edge MoS{sub 2} nanoribbons (MoS{sub 2}-ANRs) underboth the external strain and transverse electric field (E{sub t}) have been systematically investigated by using the first-principles calculations. It is found that: (1) If no electric field is applied, an interesting structural phase transition would appear under a large tensile strain, leading to a new phase MoS{sub 2}-A'NR, and inducing a big jump peak of the band gap in the transition region. But, the band gap response to compressive strains is much different from that to tensile strain, showing no the structural phase transition. (2) Under the small tensile strains (<10%), the combined E{sub t} and tensile strain give rise to a positive superposition (resonant) effect on the band gap reduction at low E{sub t} (<3 V/nm), and oppositely a negative superposition (antiresonant) one at high E{sub t} (>4 V/nm). On the other hand, the external compressive strains have always presented the resonant effect on the band gap reduction, induced by the electric field. (3) After the structural phase transition, an external large tensile strain could greatly reduce the critical field E{sub tc} causing the band gap closure, and make the system become a ferromagnetic (FM) metal at a relative low E{sub t} (e.g., <4 V/nm), which is very helpful for its promising applications in nano-mechanical spintronics devices. (4) At high E{sub t} (>10 V/nm), the magnetic moments of both the MoS{sub 2}-ANR and MoS{sub 2}-A'NR in their FM states could be enhanced greatly by a tensile strain. Our numerical results of effectively tuning physical properties of MoS{sub 2}-ANRs by combined external strain and electric field may open their new potential applications in nanoelectronics and spintronics.

  16. Suppression of thermopower of NaxCoO2 by an external magnetic field

    SciTech Connect

    Xiang, H. J.; Singh, David J

    2007-01-01

    We calculate the thermopower in Na{sub x}CoO{sub 2} using the standard Boltzmann transport theory and first principles electronic structures with spin polarization taken into account. The thermopower is found to be smaller when the system is polarized, which thereby provides an alternative reasonable explanation for the suppression of thermopower in a magnetic field. The role of the spin-orbit coupling on the thermoelectricity is also discussed.

  17. Free energy of dipolar hard spheres: The virial expansion under the presence of an external magnetic field

    NASA Astrophysics Data System (ADS)

    Elfimova, Ekaterina A.; Karavaeva, Tatyana E.; Ivanov, Alexey O.

    2014-12-01

    A method for calculation of the free energy of dipolar hard spheres under the presence of an applied magnetic field is presented. The method is based on the virial expansion in terms of density as well as the dipolar coupling constant λ, and it uses diagram technique. The formulas and the diagrams, needed to calculate the second B2 and third B3 virial coefficients, are derived up to the order of ˜λ3, and compared to the zero-field case. The formula for B2 is the same as in the zero-field case; the formula for B3, however, is different in an applied field, and a derivation is presented. This is a surprising result which is not emphasized in standard texts, but which has been noticed before in the virial expansion for flexible molecules (Caracciolo et al., 2006; Caracciolo et al., 2008). To verify the correctness of the obtained formulas, B2 and B3 were calculated within the accuracy of λ2, which were applied to initial magnetic susceptibility. The obtained expression fully coincides with the well-known theories (Morozov and Lebedev, 1990; Huke and Lücke, 2000; Ivanov and Kuznetsova, 2001), which used different methods to calculate the initial magnetic susceptibility.

  18. Adiabatic and nonadiabatic responses of the radiation belt relativistic electrons to the external changes in solar wind dynamic pressure and interplanetary magnetic field

    NASA Astrophysics Data System (ADS)

    Li, L.

    2013-12-01

    By removing the influences of 'magnetopause shadowing' (r0>6.6RE) and geomagnetic activities, we investigated statistically the responses of magnetic field and relativistic (>0.5MeV) electrons at geosynchronous orbit to 201 interplanetary perturbations during 6 years from 2003 (solar maximum) to 2008 (solar minimum). The statistical results indicate that during geomagnetically quiet times (HSYM ≥-30nT, and AE<200nT), ~47.3% changes in the geosynchronous magnetic field and relativistic electron fluxes are caused by the combined actions of the enhancement of solar wind dynamic pressure (Pd) and the southward turning of interplanetary magnetic field (IMF) (ΔPd>0.4 nPa, and IMF Bz<0 nT), and only ~18.4% changes are due to single dynamic pressure increase (ΔPd >0.4 nPa, but IMF Bz>0 nT), and ~34.3% changes are due to single southward turning of IMF (IMF Bz<0 nT, but |ΔPd|<0.4 nPa). Although the responses of magnetic field and relativistic electrons to the southward turning of IMF are weaker than their responses to the dynamic pressure increase, the southward turning of IMF can cause the dawn-dusk asymmetric perturbations that the magnetic field and the relativistic electrons tend to increase on the dawnside (LT~00:00-12:00) but decrease on the duskside (LT~13:00-23:00). Furthermore, the variation of relativistic electron fluxes is adiabatically controlled by the magnitude and elevation angle changes of magnetic field during the single IMF southward turnings. However, the variation of relativistic electron fluxes is independent of the change in magnetic field in some compression regions during the enhancement of solar wind dynamic pressure (including the single pressure increases and the combined external perturbations), indicating that nonadiabatic dynamic processes of relativistic electrons occur there. Acknowledgments. This work is supported by NSFC (grants 41074119 and 40604018). Liuyuan Li is grateful to the staffs working for the data from GOES 8-12 satellites

  19. Externally modulated theranostic nanoparticles

    PubMed Central

    Urban, Cordula; Urban, Alexander S.; Charron, Heather; Joshi, Amit

    2013-01-01

    Externally modulated nanoparticles comprise a rapidly advancing class of cancer nanotherapeutics, which combine the favorable tumor accumulation of nanoparticles, with external spatio-temporal control on therapy delivery via optical, magnetic, or ultrasound modalities. The local control on therapy enables higher tumor treatment efficacy, while simultaneously reducing off-target effects. The nanoparticle interactions with external fields have an additional advantage of frequently generating an imaging signal, and thus such agents provide theranostic (both diagnostic and therapeutic) capabilities. In this review, we classify the emerging externally modulated theranostic nanoparticles according to the mode of external control and describe the physiochemical mechanisms underlying the external control of therapy, and illustrate the major embodiments of nanoparticles in each class with proven biological efficacy: (I) electromagnetic radiation in visible and near-infrared range is being exploited for gold based and carbon nanostructures with tunable surface plasmon resonance (SPR) for imaging and photothermal therapy (PTT) of cancer, photochemistry based manipulations are employed for light sensitive liposomes and porphyrin based nanoparticles; (II) Magnetic field based manipulations are being developed for iron-oxide based nanostructures for magnetic resonance imaging (MRI) and magnetothermal therapy; (III) ultrasound based methods are primarily being employed to increase delivery of conventional drugs and nanotherapeutics to tumor sites. PMID:24834381

  20. Method of driving liquid flow at or near the free surface using magnetic microparticles

    DOEpatents

    Snezhko, Oleksiy; Aronson, Igor; Kwok, Wai-Kwong; Belkin, Maxim V.

    2011-10-11

    The present invention provides a method of driving liquid flow at or near a free surface using self-assembled structures composed of magnetic particles subjected to an external AC magnetic field. A plurality of magnetic particles are supported at or near a free surface of liquid by surface tension or buoyancy force. An AC magnetic field traverses the free surface and dipole-dipole interaction between particles produces in self-assembled snake structures which oscillate at the frequency of the traverse AC magnetic field. The snake structures independently move across the free surface and may merge with other snake structures or break up and coalesce into additional snake structures experiencing independent movement across the liquid surface. During this process, the snake structures produce asymmetric flow vortices across substantially the entirety of the free surface, effectuating liquid flow across the free surface.

  1. Two-dimensional imaging of edge-localized modes in KSTAR plasmas unperturbed and perturbed by n=1 external magnetic fields

    SciTech Connect

    Yun, G. S.; Lee, W.; Choi, M. J.; Lee, J.; Park, H. K.; Domier, C. W.; Luhmann, N. C. Jr.; Tobias, B.; Donne, A. J. H.; Lee, J. H.; Jeon, Y. M.; Yoon, S. W.; Collaboration: KSTAR Team

    2012-05-15

    The temporal evolution of edge-localized modes (ELMs) has been studied using a 2-D electron cyclotron emission imaging system in the KSTAR tokamak. The ELMs are observed to evolve in three distinctive stages: the initial linear growth of multiple filamentary structures having a net poloidal rotation, the interim state of regularly spaced saturated filaments, and the final crash through a short transient phase characterized by abrupt changes in the relative amplitudes and distance among filaments. The crash phase, typically consisted of multiple bursts of a single filament, involves a complex dynamics, poloidal elongation of the bursting filament, development of a fingerlike bulge, and fast localized burst through the finger. Substantial alterations of the ELM dynamics, such as mode number, poloidal rotation, and crash time scale, have been observed under external magnetic perturbations with the toroidal mode number n= 1.

  2. Dynamic phase transitions of the Blume-Emery-Griffiths model under an oscillating external magnetic field by the path probability method

    NASA Astrophysics Data System (ADS)

    Ertaş, Mehmet; Keskin, Mustafa

    2015-03-01

    By using the path probability method (PPM) with point distribution, we study the dynamic phase transitions (DPTs) in the Blume-Emery-Griffiths (BEG) model under an oscillating external magnetic field. The phases in the model are obtained by solving the dynamic equations for the average order parameters and a disordered phase, ordered phase and four mixed phases are found. We also investigate the thermal behavior of the dynamic order parameters to analyze the nature dynamic transitions as well as to obtain the DPT temperatures. The dynamic phase diagrams are presented in three different planes in which exhibit the dynamic tricritical point, double critical end point, critical end point, quadrupole point, triple point as well as the reentrant behavior, strongly depending on the values of the system parameters. We compare and discuss the dynamic phase diagrams with dynamic phase diagrams that were obtained within the Glauber-type stochastic dynamics based on the mean-field theory.

  3. Effect of the external field on the soft magnetic properties and microstructure of directly cast Fe75P8.7B5C7Si4.3 nanocrystalline sheets

    NASA Astrophysics Data System (ADS)

    Shih, C. W.; Lin, Y. Y.; Chang, H. W.; Lee, Y. I.; Chang, W. C.; Yang, C. C.

    2015-05-01

    A new method to fabricate soft magnetic bulk metallic glasses (BMGs) by an injection casting with applying external magnetic field during solidification has been developed. The effect of applying magnetic fields (Ha) on soft magnetic properties and microstructure of Fe75P8.7B5C7Si4.3 alloy sheets with dimension of t × 4 mm × 15 mm (t = 1-3 mm) have been studied. The microstructure shows that the fully amorphous is attained by the applying magnetic field even at the core region of the thicker sheets with t = 3 mm. All studied sheets exhibit similar saturation magnetization of 1.23-1.25 T, but the coercivity and resistivity are strongly dependent on the thickness t and the strength of magnetic field Ha, where Hc increases with t, the slope of Hc versus t decreases with the increase of Ha, and the resistivity increases with the increase of Ha. The changes of coercivity and resistivity are strongly related to the fully amorphous induced by Ha. The external magnetic field has significant improvement in glass forming ability, and thus coercivity and resistivity for the studied sheet, especially for larger t = 3 mm. This study suggests that applying a magnetic field during the casting process provides a useful way to produce high-performance magnetically soft Fe-based BMGs.

  4. Evaluating foot kinematics using magnetic resonance imaging: from maximum plantar flexion, inversion, and internal rotation to maximum dorsiflexion, eversion, and external rotation.

    PubMed

    Fassbind, Michael J; Rohr, Eric S; Hu, Yangqiu; Haynor, David R; Siegler, Sorin; Sangeorzan, Bruce J; Ledoux, William R

    2011-10-01

    The foot consists of many small bones with complicated joints that guide and limit motion. A variety of invasive and noninvasive means [mechanical, X-ray stereophotogrammetry, electromagnetic sensors, retro-reflective motion analysis, computer tomography (CT), and magnetic resonance imaging (MRI)] have been used to quantify foot bone motion. In the current study we used a foot plate with an electromagnetic sensor to determine an individual subject's foot end range of motion (ROM) from maximum plantar flexion, internal rotation, and inversion to maximum plantar flexion, inversion, and internal rotation to maximum dorsiflexion, eversion, and external rotation. We then used a custom built MRI-compatible device to hold each subject's foot during scanning in eight unique positions determined from the end ROM data. The scan data were processed using software that allowed the bones to be segmented with the foot in the neutral position and the bones in the other seven positions to be registered to their base positions with minimal user intervention. Bone to bone motion was quantified using finite helical axes (FHA). FHA for the talocrural, talocalcaneal, and talonavicular joints compared well to published studies, which used a variety of technologies and input motions. This study describes a method for quantifying foot bone motion from maximum plantar flexion, inversion, and internal rotation to maximum dorsiflexion, eversion, and external rotation with relatively little user processing time. PMID:22070336

  5. The Effects of Magnetic Nanoparticles on Magnetic Fluid Hyperthermia

    NASA Astrophysics Data System (ADS)

    Liangruksa, Monrudee; Kappiyoor, Ravi; Ganguly, Ranjan; Puri, Ishwar

    2010-11-01

    Magnetic fluid hyperthermia (MFH) is a cancer treatment in which biocompatible magnetic nanoparticles are dispersed into a tumor and heated by an external AC magnetic field. Over a period of time, the tumor cells are locally heated, leading to hyperthermia which damages and kills the tumor cells with minimal damage to the surrounding normal tissue. The applied magnetic field must be high enough to induce hyperthermia for a specified magnetic particle concentration in the tumor but also lies within the safe limit for human exposure. Six materials, barium ferrite, cobalt ferrite, iron-cobalt, iron-platinum, magnetite and maghemite, are considered as candidates for MFH use. We find that fcc iron-platinum, magnetite and maghemite generate useful treatment temperatures and, when included in a ferrofluid, can produce sufficient and effective MFH for which optimal conditions are explored.

  6. Aging and magnetism: Presenting a possible new holistic paradigm for ameliorating the aging process and the effects thereof, through externally applied physiologic PicoTesla magnetic fields.

    PubMed

    Jacobson, Jerry; Sherlag, Benjamin

    2015-09-01

    A new holistic paradigm is proposed for slowing our genomic-based biological clocks (e.g. regulation of telomere length), and decreasing heat energy exigencies for maintenance of physiologic homeostasis. Aging is considered the result of a progressive slow burn in small volumes of tissues with increase in the quantum entropic states; producing desiccation, microscopic scarring, and disruption of cooperative coherent states. Based upon piezoelectricity, i.e. photon-phonon transductions, physiologic PicoTesla range magnetic fields may decrease the production of excessive heat energy through target specific, bio molecular resonant interactions, renormalization of intrinsic electromagnetic tissue profiles, and autonomic modulation. Prospectively, we hypothesize that deleterious effects of physical trauma, immunogenic microbiological agents, stress, and anxiety may be ameliorated. A particle-wave equation is cited to ascertain magnetic field parameters for application to the whole organism thereby achieving desired homeostasis; secondary to restoration of structure and function on quantum levels. We hypothesize that it is at the atomic level that physical events shape the flow of signals and the transmission of energy in bio molecular systems. References are made to experimental data indicating the aspecific efficacy of non-ionizing physiologic magnetic field profiles for treatment of various pathologic states. PMID:26092501

  7. Externally triggered microcapsules

    NASA Technical Reports Server (NTRS)

    Morrison, Dennis R. (Inventor); Mosier, Benjamin (Inventor)

    2011-01-01

    Disclosed are microcapsules comprising a polymer shell enclosing one or more immiscible liquid phases in which a drug or drug precursor are contained in a liquid phase. The microparticles also contain magnetic particles that can be heated by application of an external magnetic field and thus heated to a predetermined Curie temperature. Heating of the particles melts the polymer shell and releases the drug without causing heating of surrounding tissues.

  8. Entanglement and Teleportation via Thermally Entangled State of Anisotropic Heisenberg XYZ Chain with Inhomogeneous External Magnetic Field

    NASA Astrophysics Data System (ADS)

    Ni, Hui-Ying; Fang, Jian-Xing; Zhu, Shi-Qun; Sha, Jin-Qiao; Jiang, Wei-Xing

    2008-02-01

    In this paper we study the entanglement in a two-qubit spin in the XYZ model, and teleport a two-qubit entangled state using this spin chain in the condition of the thermal equilibrium as a quantum channel. We investigate the effects of the interaction of z-component JZ, the inhomogeneous magnetic field b, the anisotropy γ, and the temperature T on the entanglement and fidelity. In order to characterize the quality of the teleported state, we research the average fidelity Fa. High average fidelity of the teleportation is obtained when the temperat ure is very low. Under some condition, we also find that when inhomogeneity increases to a certain value, the average fidelity can exhibit a larger revival than that for less values of b.

  9. Kinetic description of a degenerate, rotating, non-neutral electron plasma in external magnetic fields in the framework of the Thomas-Fermi-Dirac theory

    NASA Astrophysics Data System (ADS)

    Molinari, V. G.; Rocchi, F.; Sumini, M.

    2002-01-01

    Aim of this work is to extend the results obtained in a previous study on the magnetic confinement and stability of a quantum degenerate non-neutral fermion plasma. This extension consists in the inclusion in the previously set up model of the effects of the exchange forces, and generalises the Thomas-Fermi (TF) approach used in the referenced work towards a Thomas-Fermi-Dirac (TFD) statistical description. The TF model has not only been used extensively and with success in these years to study atomic, nuclear and molecular properties, or to evaluate features of matter in extreme conditions such as low temperatures and/or high densities typical of astrophysics and inertial confinement fusion experiments, but also to found hydrodynamic theories for the diffusion and stability of fermion plasmas, one component non-neutral degenerate fluids, plasmas etc. In this paper an equation for density profiles in cylindrical symmetry is found, from the semiclassical kinetic theory of quantum gases, which takes into account the effects of temperature, average velocity, external magnetic field and quantum exchange. Numerical solutions of this equation for the case of complete quantum degeneracy are given and comparisons with the previous results are carried out.

  10. In vitro T lymphocyte adherence capabilities under the influence of lower induction values (0.1 - 0.01 mT) of 50 Hz external magnetic fields

    NASA Astrophysics Data System (ADS)

    Čoček, A.; Jandová, A.; Hahn, A.; Mártonová, J.; Ambruš, M.; Dohnalová, A.; Nedbalová, M.; Pokorný, J.

    2011-12-01

    Our research thus far has concerned the impact of external magnetic fields (50 Hz) and low (0.01-10 mT) induction on adherence capabilities of T lymphocytes obtained from the blood of patients with head and neck tumors. We know that the in vitro adherence capability of T lymphocytes towards surfaces in cancer patients is less than that of control. Previously, we have found that exposure to magnetic fields (50 Hz / 0.01-10 mT) increases the capability of T lymphocytes, in larynx/pharynx cancer patients, to adhere in vitro to surfaces, achieving almost physiological values, in not only pre-treatment patients but also those receiving treatment in the course of follow-up. The capability of T lymphocytes in controls (voluntary blood donors) to adhere to surfaces was also increased (50 Hz / 0.01-0.5 mT). The present study concentrates on the significance of the level of magnetic field induction in order to determine whether low induction values can restore T lymphocytes adherence capabilities. Testing a set of 20 patients showed a statistically significant difference (p < 0.05) in the in vitro adherence capacity of T lymphocytes between both 0.01 and 0.05, and 0.1 mT induction levels. In the control group (patients diagnosed with chronic sensorineural hearing loss) there was even a statistically significant difference between induction values of 0.05 and 0.01 mT. Therefore, we concluded that lower induction values resulted in a more biologically significant response.

  11. Role of spin-orbit coupling and evolution of the electronic structure of WTe2 under an external magnetic field

    NASA Astrophysics Data System (ADS)

    Rhodes, D.; Das, S.; Zhang, Q. R.; Zeng, B.; Pradhan, N. R.; Kikugawa, N.; Manousakis, E.; Balicas, L.

    2015-09-01

    Here, we present a detailed study on the temperature and angular dependence of the Shubnikov-de Haas (SdH) effect in the semimetal WTe2. This compound was recently shown to display a very large nonsaturating magnetoresistance which was attributed to nearly perfectly compensated densities of electrons and holes. We observe four fundamental SdH frequencies and attribute them to spin-orbit split, electron-like, and hole-like Fermi-surface (FS) cross-sectional areas. Their angular dependence seems consistent with ellipsoidal FSs with volumes suggesting a modest excess in the density of electrons with respect to that of the holes. We show that density functional theory (DFT) calculations fail to correctly describe the FSs of WTe2. When their cross-sectional areas are adjusted to reflect the experimental data, the resulting volumes of the electron/hole FSs obtained from the DFT calculations would imply a pronounced imbalance between the densities of electrons and holes. We find evidence for field-dependent Fermi-surface cross-sectional areas by fitting the oscillatory component superimposed onto the magnetoresistivity signal to several Lifshitz-Kosevich components. We also observe a pronounced field-induced renormalization of the effective masses. Taken together, our observations suggest that the electronic structure of WTe2 evolves with the magnetic field due to the Zeeman splitting. This evolution is likely to contribute to its pronounced magnetoresistivity.

  12. Role of spin-orbit coupling and evolution of the electronic structure of WTe2 under an external magnetic field

    NASA Astrophysics Data System (ADS)

    Rhodes, Daniel; Das, Suvadip; Zhang, Qiu Run; Zeng, Bin; Pradhan, Nihar; Kikugawa, Naoki; Manousakis, Efstratios; Balicas, Luis

    Here, we present a study on the temperature and angular dependence of the Shubnikov-de Haas (SdH) effect in the semimetal WTe2. This compound has been shown to display a large, nonsaturating magnetoresistance which was attributed to nearly perfectly compensated densities of electrons and holes. We observe four fundamental SdH frequencies and attribute them to spin-orbit split, electron-like, and hole-like Fermi-surface (FS) cross-sectional areas. Their angular dependence is consistent with ellipsoidal FSs that suggest a modest excess in the density of electrons with respect to that of the holes. We show that DFT calculations fail to correctly describe the FSs of WTe2 and find evidence for field-dependent FS cross-sectional areas. We also observe a pronounced field-induced renormalization of the effective masses. Our observations suggest that the electronic structure of WTe2 evolves with the magnetic field due to the Zeeman splitting. This evolution is likely to contribute to its pronounced magnetoresistivity. The work was supported by NSF through Grant No. NSFDMR-1157490, the state of Florida, DOE-BES through award No. DE-SC0002613 and by the Army Research Office through MURI Grant No. W911NF-11-10362.

  13. Investigation of magnetic spin glass property in La{sub 0.5}Bi{sub 0.5}MnO{sub 3} sample using non-linear AC susceptibility measurements

    SciTech Connect

    Kumar, Punith V. Manju, M. R. Dayal, Vijaylakshmi

    2014-04-24

    We present a comprehensive study on origin of Spin Glass (SG) property in polycrystalline La{sub 0.5}Bi{sub 0.5}MnO{sub 3} perovskite oxide using linear and higher order ac susceptibility (χ) measurements. The third order harmonic susceptibility (χ{sub 3}) vs. temperature (K) with varying magnetic fields from 0.95 to 9.45 Oe and the divergence in their χ{sub 3} (max) allows us to infer the SG behavior occurring in the sample possibly due to co-operative freezing of the spins.

  14. A study of K shell X-ray intensity ratios of NixCr1-x alloys in external magnetic field and determination of effective atomic numbers of these alloys

    NASA Astrophysics Data System (ADS)

    Perişanoğlu, Ufuk; Demir, Lütfü

    2015-05-01

    In this study, the effect of external magnetic field on the Kβ/Kα X-ray intensity ratios of various alloy compositions of Ni-Cr transition metal alloys has been investigated. The Kα and Kβ emission spectra of Ni, Cr and NixCr1-x (x=0.40; 0.50; 0.60; 0.80) alloys were measured by using a Si (Li) solid-state detector. Kβ/Kα X-ray intensity ratios of Ni, Cr and NixCr1-x alloys without magnetic field and in 0.5 and 1 T external magnetic field have been measured following excitation by 59.5 keV γ-rays from a 200 mCi241Am radioisotope point source. When the experimental data obtained in external magnetic field have been compared with data without external magnetic field, deviations have been observed in Kβ/Kα X-ray intensity ratios for Ni and Cr in different alloy compositions. Thus, results of these measurements have shown that Kβ/Kα X-ray intensity ratios of Ni and Cr in NixCr1-x alloys are dependent on the external magnetic field. Also the total mass attenuation coefficients for pure 3d transition metals and their alloys at different compositions were measured and theoretically estimated using mixture rule for selected photon energy. Later on, total atomic and electronic cross-sections and effective atomic number for alloys are determined experimentally and theoretically using these mass attenuation coefficients. When these parameters are examined depending on the alloy compositions, thereof have been found to vary with the alloy composition.

  15. Sensitivity degradation of an anger camera operated in SPECT-like mode under the influence of a strong external magnetic field

    NASA Astrophysics Data System (ADS)

    Galiano, Eduardo; Aldarwish, Huda

    2014-11-01

    The purpose of this work was to experimentally determine the degradation in sensitivity of an Anger camera rotated in SPECT-like orbits around the transverse and sagittal planes of the magnetic field produced by a conventional, dual coil, 1 T electromagnet. A 74 photomultiplier Siemens Basicam Anger camera with a 29 cm radius crystal and an Isotrak 35 cm diameter, 46 MBq (1.25 mCi), Co-57 disk source attached to a low energy general purpose collimator, were used for all measurements. A custom made, air-cooled, dual coil, 1 T electromagnet was used to produce the external magnetic field. A map of the magnetic field was obtained by taking intensity measurements around the sagittal and transverse planes of the magnet. Camera sensitivity - defined as the measured count rate for a given activity of a radionuclide in a defined geometry - was first measured around the transverse plane at angles of 0°, 90°, and 270°, with, and without, the magnetic field present. At each angle, three 30 min measurements were made and the average count rate was calculated. A similar protocol was used for measurements upon rotation in the sagittal plane: counts per 30 min interval were measured for 20 angles, with a 15° increment between measurements. Camera sensitivity as a function of field strength was also determined by collecting counts over 30 min intervals at a fixed angle (90°) with magnet currents of 0.00 A, 2.65 A, and 5.30 A. In the transverse plane, at 0° under a field intensity of 21 mT, the loss in sensitivity was 18.14%, at 90° (B=37 mT) the loss was 30.5%, and at 270° (B=38 mT) the loss was 34.9%. Thus for rotation in the transverse plane, the sensitivity is monotonically reduced with an increase in field intensity. On rotation in the sagittal plane, sensitivity degradation ranged between 50.3% at a 22° angle, and 59.1% at 315°. Broad sensitivity peaks were observed at 105° and 195°, with minima at 60°, 135°, and 260°, consistent with our theoretical

  16. Temperature evolution of superparamagnetic clusters in single-crystal La0.85Sr0.15CoO3 characterized by nonlinear magnetic ac response and neutron depolarization

    NASA Astrophysics Data System (ADS)

    Lazuta, A. V.; Ryzhov, V. A.; Runov, V. V.; Khavronin, V. P.; Deriglazov, V. V.

    2015-07-01

    The representative measurements of the second harmonic in ac magnetization complemented by neutron depolarization have been performed for single-crystal La0.85Sr0.15CoO3 in the temperature range 97 KMagnetic, geometrical, and dynamical parameters of the FMC system have been evaluated in the temperature range T <140 K, where superparamagnetic regime installs, by means of the formalism involving the Fokker-Planck equation. With lowering the temperature, the amount of clusters fraction, the cluster size, and magnetic moment along with its diffusion relaxation time strongly increase, each in its own temperature interval. Below 130 K, FMC contribute essentially to the total linear magnetic susceptibility. The damping factor of the order 10-1 proves the importance of precession in thermal relaxation of the cluster magnetic moment. The FMC are a precursor of long-range ferromagnetic correlations seen below 100 K with neutron-scattering techniques.

  17. Effect of external magnetic field on valence-electron structures of Fe and Ni in Invar, Permalloy and the other Fe-Ni alloys by using Kβ-to-Kα X-ray intensity ratios.

    PubMed

    Alım, Bünyamin; Han, İbrahim; Demir, Lütfü

    2016-06-01

    The effect of external magnetic field on the valence-electron structures of Fe and Ni in various Fe-Ni alloy compositions was investigated by using X-ray fluorescence spectroscopy. Firstly, Kβ-to-Kα X-ray intensity ratios of Fe and Ni in Invar (Fe0.64Ni0.36), Permalloy (Fe0.20Ni0.80) and FexNi1-x (x=0, 0.40, 0.52, 0.55, 0.61, and 1) alloys were measured without any magnetic field and under 0.5 and 1T external magnetic fields, separately. Later, the valence-electron structures of Fe and Ni in both pure form and alloys were obtained by comparison of measured X-ray intensity ratios with the results of multi-configurations Dirac-Fock (MCDF) calculations. The results obtained for valence-electron structures of Fe and Ni in various Fe-Ni alloys were evaluated in terms of magnetic field effect, delocalization and/or charge transfer phenomena. The results have shown that valence electron structure of Fe and Ni in Fe-Ni alloys are dependent on both external magnetic field and concentration of alloy elements. PMID:26974486

  18. Electrogenerated chemiluminescence immunosensor for Bacillus thuringiensis Cry1Ac based on Fe3O4@Au nanoparticles.

    PubMed

    Li, Jianping; Xu, Qian; Wei, Xiaoping; Hao, Zaibin

    2013-02-20

    A highly sensitive electrochemiluminescence (ECL) immunosensor for Cry1Ac was fabricated. The primary antibody anti-Cry1Ac was immobilized onto core-shell structural Fe(3)O(4)@Au nanoparticles. The antigen and glucose-oxidase-labeled secondary antibody were then successively combined to form sandwich-type immunocomplexes through a specific interaction. The magnetic particles loaded with sandwich immune complexes were attracted to a magnet-controlled glass carbon electrode (GCE) by an external magnet applied on top of the GCE. ECL was generated by the reaction between luminol and hydrogen peroxide derived from the enzymatic reaction in the presence of glucose. The sensors exhibited high sensitivity and a wide linear range for Bacillus thuringiensis Cry1Ac detection from 0 to 6 ng/mL, as well as a detection limit of 0.25 pg/mL (S/N = 3). The sensor is one of the most sensitive sensors for Cry1Ac, which can be easily renewed and conveniently used. PMID:23317307

  19. RHIC AC DIPOLE DESIGN AND CONSTRUCTION.

    SciTech Connect

    BAI,M.; METH,M.; PAI,C.; PARKER,B.; PEGGS,S.; ROSER,T.; SANDERS,R.; TRBOJEVIC,D.; ZALTSMAN,A.

    2001-06-18

    Two ac dipoles with vertical and horizontal magnetic field have been proposed at RHIC for applications in linear and non-linear beam dynamics and spin manipulations. A magnetic field amplitude of 380 Gm is required to produce a coherent oscillation of 5 times the rms beam size at the top energy. We take the ac dipole frequency to be 1.0% of the revolution frequency away from the betatron frequency. To achieve the strong magnetic field with minimum power loss, an air-core magnet with two seven turn winding of low loss Litz wire resonating at 64 kHz is designed. The system is also designed to allow one to connect the two magnet winding in series to resonate at 37 kHz for the spin manipulation. Measurements of a half length prototype magnet are also presented.

  20. AC losses and heat removal in three-dimensional winding pack of Samsung superconducting test facility under pulsed magnetic field operation

    NASA Astrophysics Data System (ADS)

    Wang, Qiuliang; Seong Yoon, Cheon; Baang, Sungkeun; Kim, Myungkyu; Park, Hyunki; Kim, Yongjin; Lee, Sangil; Kim, Keeman

    2001-04-01

    The Samsung superconducting test facility (SSTF) will be operated under the highly pulsed field to simulate the operating conditions of KSTAR. An analysis has been performed to study the transient heat removal characteristics and temperature margin for the main, blip and compensating coils in the SSTF. This method is based on a quasi-three-dimensional model, which the thermal coupling of turn-to-turn, pancake-to-pancake and channel-to-channel is taken into account, to simulate the conductor temperature rise and the thermal expansion of supercritical helium due to the high AC losses under the pulsed field. The local AC losses, which include coupling loss, eddy current loss and hysteresis loss in the cable-in-conduit conductor, are estimated. The temperature margin, mass flow rate, distribution of AC losses are studied under the given operating scenario. The mass flow reduction and peak temperature rise depending on the inlet pressure and inlet position of CICC are studied. It is shown that the initial mass flow rate remarkably influences on the peak temperature of superconducting strands. The large mass flow rate can reduce the temperature rise when the inlet of helium is located at the high field region. By contrast, because of heat induced flow to improve the cooling condition of the superconducting strands, the small initial mass flow rate results in the low peak temperature in strands when the inlet of helium is located at the low field region.